feat: add PWA install prompt UI (#35)

- Create usePWAInstall composable for install management
- Add InstallPrompt banner component with auto-show after 3s
- Add App Settings tab in settings page
- Show install button with loading state
- Display installation status and instructions
- Handle dismissal with 7-day cooldown
- Add iOS/Android installation guides
- Show PWA features list
- Display storage usage with visual progress
- Auto-hide prompt after successful install

Features:
- Automatic install prompt after 3 seconds
- Manual install from settings
- Platform-specific instructions
- Smart dismissal tracking
- Storage info visualization

Closes #35

app/app/app.vue

@@ -1,6 +1,7 @@
 <template>
   <div>
     <OfflineBanner />
+    <InstallPrompt />
     <NuxtLayout>
       <NuxtPage />
     </NuxtLayout>

app/components/InstallPrompt.vue

@@ -0,0 +1,104 @@
+<template>
+  <Transition
+    enter-active-class="transition ease-out duration-300"
+    enter-from-class="opacity-0 translate-y-2"
+    enter-to-class="opacity-100 translate-y-0"
+    leave-active-class="transition ease-in duration-200"
+    leave-from-class="opacity-100 translate-y-0"
+    leave-to-class="opacity-0 translate-y-2"
+  >
+    <div
+      v-if="showPrompt"
+      class="fixed bottom-4 left-4 right-4 md:left-auto md:right-4 md:max-w-md z-50"
+    >
+      <div class="bg-white dark:bg-gray-800 rounded-xl shadow-2xl border border-gray-200 dark:border-gray-700 p-4">
+        <div class="flex items-start gap-4">
+          <!-- App Icon -->
+          <div class="flex-shrink-0">
+            <img 
+              src="/icon-192x192.png" 
+              alt="Pantry icon" 
+              class="w-16 h-16 rounded-lg shadow-md"
+            />
+          </div>
+          
+          <!-- Content -->
+          <div class="flex-1 min-w-0">
+            <h3 class="text-lg font-bold text-gray-900 dark:text-white mb-1">
+              Install Pantry
+            </h3>
+            <p class="text-sm text-gray-600 dark:text-gray-400 mb-3">
+              Install this app for quick access and offline use
+            </p>
+            
+            <!-- Actions -->
+            <div class="flex gap-2">
+              <UButton
+                color="emerald"
+                size="sm"
+                @click="install"
+                :loading="installing"
+              >
+                <template #leading>
+                  <UIcon name="i-heroicons-arrow-down-tray" />
+                </template>
+                Install
+              </UButton>
+              
+              <UButton
+                color="gray"
+                variant="ghost"
+                size="sm"
+                @click="dismiss"
+              >
+                Not now
+              </UButton>
+            </div>
+          </div>
+          
+          <!-- Close button -->
+          <button
+            @click="dismiss"
+            class="flex-shrink-0 text-gray-400 hover:text-gray-600 dark:hover:text-gray-300 transition"
+          >
+            <UIcon name="i-heroicons-x-mark" class="w-5 h-5" />
+          </button>
+        </div>
+      </div>
+    </div>
+  </Transition>
+</template>
+
+<script setup lang="ts">
+const { canInstall, promptInstall, dismissInstall, shouldShowPrompt } = usePWAInstall()
+const installing = ref(false)
+const showPrompt = ref(false)
+
+// Show prompt after a delay if conditions are met
+onMounted(() => {
+  setTimeout(() => {
+    if (shouldShowPrompt()) {
+      showPrompt.value = true
+    }
+  }, 3000) // Wait 3 seconds after page load
+})
+
+async function install() {
+  installing.value = true
+  try {
+    const { outcome } = await promptInstall()
+    if (outcome === 'accepted') {
+      showPrompt.value = false
+    }
+  } catch (error) {
+    console.error('Install failed:', error)
+  } finally {
+    installing.value = false
+  }
+}
+
+function dismiss() {
+  dismissInstall()
+  showPrompt.value = false
+}
+</script>

app/components/Settings/AppSettings.vue

@@ -0,0 +1,190 @@
+<template>
+  <UCard class="mt-4">
+    <div class="space-y-6">
+      <div>
+        <h3 class="text-lg font-semibold mb-4">App Installation</h3>
+        
+        <!-- Already installed -->
+        <div v-if="isInstalled" class="flex items-start gap-3 p-4 bg-emerald-50 dark:bg-emerald-900/20 rounded-lg">
+          <UIcon name="i-heroicons-check-circle" class="w-6 h-6 text-emerald-600 dark:text-emerald-400 flex-shrink-0 mt-0.5" />
+          <div>
+            <p class="font-medium text-emerald-900 dark:text-emerald-100">
+              App is installed
+            </p>
+            <p class="text-sm text-emerald-700 dark:text-emerald-300 mt-1">
+              You're using Pantry as an installed app with offline support.
+            </p>
+          </div>
+        </div>
+
+        <!-- Can install -->
+        <div v-else-if="canInstall" class="space-y-3">
+          <p class="text-gray-600 dark:text-gray-400">
+            Install Pantry as an app for quick access and offline use.
+          </p>
+          <UButton
+            color="emerald"
+            size="lg"
+            @click="install"
+            :loading="installing"
+            block
+          >
+            <template #leading>
+              <UIcon name="i-heroicons-arrow-down-tray" />
+            </template>
+            Install App
+          </UButton>
+        </div>
+
+        <!-- Not supported or already running -->
+        <div v-else class="space-y-4">
+          <div v-if="isStandalone" class="flex items-start gap-3 p-4 bg-blue-50 dark:bg-blue-900/20 rounded-lg">
+            <UIcon name="i-heroicons-information-circle" class="w-6 h-6 text-blue-600 dark:text-blue-400 flex-shrink-0 mt-0.5" />
+            <div>
+              <p class="font-medium text-blue-900 dark:text-blue-100">
+                Running as standalone app
+              </p>
+              <p class="text-sm text-blue-700 dark:text-blue-300 mt-1">
+                You're already using Pantry in standalone mode.
+              </p>
+            </div>
+          </div>
+
+          <div v-else>
+            <p class="text-gray-600 dark:text-gray-400 mb-4">
+              Installation is not available yet. Try one of these options:
+            </p>
+            
+            <!-- iOS Instructions -->
+            <UCard class="mb-4">
+              <div class="flex items-start gap-3">
+                <UIcon name="i-heroicons-device-phone-mobile" class="w-6 h-6 text-gray-400 flex-shrink-0 mt-0.5" />
+                <div class="flex-1">
+                  <h4 class="font-semibold mb-2">iOS (Safari)</h4>
+                  <ol class="text-sm text-gray-600 dark:text-gray-400 space-y-1 list-decimal list-inside">
+                    <li>Tap the Share button</li>
+                    <li>Scroll down and tap "Add to Home Screen"</li>
+                    <li>Tap "Add" to confirm</li>
+                  </ol>
+                </div>
+              </div>
+            </UCard>
+
+            <!-- Android Instructions -->
+            <UCard>
+              <div class="flex items-start gap-3">
+                <UIcon name="i-heroicons-device-phone-mobile" class="w-6 h-6 text-gray-400 flex-shrink-0 mt-0.5" />
+                <div class="flex-1">
+                  <h4 class="font-semibold mb-2">Android (Chrome)</h4>
+                  <ol class="text-sm text-gray-600 dark:text-gray-400 space-y-1 list-decimal list-inside">
+                    <li>Tap the menu (⋮) button</li>
+                    <li>Tap "Add to Home screen" or "Install app"</li>
+                    <li>Tap "Install" to confirm</li>
+                  </ol>
+                </div>
+              </div>
+            </UCard>
+          </div>
+        </div>
+      </div>
+
+      <!-- PWA Features -->
+      <div>
+        <h3 class="text-lg font-semibold mb-3">App Features</h3>
+        <div class="space-y-2">
+          <div class="flex items-center gap-2 text-gray-700 dark:text-gray-300">
+            <UIcon name="i-heroicons-check" class="w-5 h-5 text-emerald-500" />
+            <span>Works offline with cached data</span>
+          </div>
+          <div class="flex items-center gap-2 text-gray-700 dark:text-gray-300">
+            <UIcon name="i-heroicons-check" class="w-5 h-5 text-emerald-500" />
+            <span>Quick access from home screen</span>
+          </div>
+          <div class="flex items-center gap-2 text-gray-700 dark:text-gray-300">
+            <UIcon name="i-heroicons-check" class="w-5 h-5 text-emerald-500" />
+            <span>Full-screen experience</span>
+          </div>
+          <div class="flex items-center gap-2 text-gray-700 dark:text-gray-300">
+            <UIcon name="i-heroicons-check" class="w-5 h-5 text-emerald-500" />
+            <span>Automatic updates</span>
+          </div>
+        </div>
+      </div>
+
+      <!-- Storage Info -->
+      <div v-if="storageInfo">
+        <h3 class="text-lg font-semibold mb-3">Storage Usage</h3>
+        <div class="space-y-2">
+          <div class="flex justify-between text-sm">
+            <span class="text-gray-600 dark:text-gray-400">Used</span>
+            <span class="font-medium">{{ formatBytes(storageInfo.usage) }}</span>
+          </div>
+          <div class="flex justify-between text-sm">
+            <span class="text-gray-600 dark:text-gray-400">Available</span>
+            <span class="font-medium">{{ formatBytes(storageInfo.quota) }}</span>
+          </div>
+          <div class="w-full bg-gray-200 dark:bg-gray-700 rounded-full h-2">
+            <div 
+              class="bg-emerald-500 h-2 rounded-full transition-all"
+              :style="{ width: storagePercent + '%' }"
+            />
+          </div>
+        </div>
+      </div>
+    </div>
+  </UCard>
+</template>
+
+<script setup lang="ts">
+const { canInstall, isInstalled, promptInstall } = usePWAInstall()
+const installing = ref(false)
+const storageInfo = ref<{ usage: number; quota: number } | null>(null)
+
+const isStandalone = computed(() => {
+  if (process.client) {
+    return window.matchMedia('(display-mode: standalone)').matches
+  }
+  return false
+})
+
+const storagePercent = computed(() => {
+  if (!storageInfo.value) return 0
+  return Math.round((storageInfo.value.usage / storageInfo.value.quota) * 100)
+})
+
+async function install() {
+  installing.value = true
+  try {
+    await promptInstall()
+  } catch (error) {
+    console.error('Install failed:', error)
+  } finally {
+    installing.value = false
+  }
+}
+
+function formatBytes(bytes: number): string {
+  if (bytes === 0) return '0 Bytes'
+  const k = 1024
+  const sizes = ['Bytes', 'KB', 'MB', 'GB']
+  const i = Math.floor(Math.log(bytes) / Math.log(k))
+  return Math.round((bytes / Math.pow(k, i)) * 100) / 100 + ' ' + sizes[i]
+}
+
+onMounted(async () => {
+  // Get storage info
+  if ('storage' in navigator && 'estimate' in navigator.storage) {
+    try {
+      const estimate = await navigator.storage.estimate()
+      if (estimate.usage !== undefined && estimate.quota !== undefined) {
+        storageInfo.value = {
+          usage: estimate.usage,
+          quota: estimate.quota
+        }
+      }
+    } catch (error) {
+      console.error('Failed to get storage estimate:', error)
+    }
+  }
+})
+</script>

app/composables/usePWAInstall.ts

@@ -0,0 +1,93 @@
+/**
+ * Composable to handle PWA installation
+ * 
+ * Usage:
+ * const { canInstall, isInstalled, promptInstall, dismissInstall } = usePWAInstall()
+ */
+export function usePWAInstall() {
+  const canInstall = ref(false)
+  const isInstalled = ref(false)
+  const deferredPrompt = ref<any>(null)
+
+  if (process.client) {
+    // Check if already installed
+    if (window.matchMedia('(display-mode: standalone)').matches) {
+      isInstalled.value = true
+    }
+
+    // Listen for beforeinstallprompt event
+    window.addEventListener('beforeinstallprompt', (e) => {
+      // Prevent the mini-infobar from appearing on mobile
+      e.preventDefault()
+      
+      // Stash the event so it can be triggered later
+      deferredPrompt.value = e
+      canInstall.value = true
+    })
+
+    // Listen for appinstalled event
+    window.addEventListener('appinstalled', () => {
+      isInstalled.value = true
+      canInstall.value = false
+      deferredPrompt.value = null
+    })
+  }
+
+  async function promptInstall() {
+    if (!deferredPrompt.value) {
+      return { outcome: 'not-available' }
+    }
+
+    // Show the install prompt
+    deferredPrompt.value.prompt()
+
+    // Wait for the user to respond to the prompt
+    const { outcome } = await deferredPrompt.value.userChoice
+
+    // Clear the deferredPrompt
+    deferredPrompt.value = null
+    
+    if (outcome === 'accepted') {
+      canInstall.value = false
+    }
+
+    return { outcome }
+  }
+
+  function dismissInstall() {
+    canInstall.value = false
+    deferredPrompt.value = null
+    
+    // Remember dismissal for 7 days
+    if (process.client) {
+      localStorage.setItem('pwa-install-dismissed', Date.now().toString())
+    }
+  }
+
+  function shouldShowPrompt() {
+    if (!canInstall.value || isInstalled.value) {
+      return false
+    }
+
+    if (process.client) {
+      const dismissed = localStorage.getItem('pwa-install-dismissed')
+      if (dismissed) {
+        const dismissedTime = parseInt(dismissed)
+        const sevenDays = 7 * 24 * 60 * 60 * 1000
+        if (Date.now() - dismissedTime < sevenDays) {
+          return false
+        }
+      }
+    }
+
+    return true
+  }
+
+  return {
+    canInstall: readonly(canInstall),
+    isInstalled: readonly(isInstalled),
+    promptInstall,
+    dismissInstall,
+    shouldShowPrompt
+  }
+}

app/pages/settings.vue

@@ -18,6 +18,10 @@
         </div>
       </template>
 
+      <template #app>
+        <SettingsAppSettings />
+      </template>
+
       <template #about>
         <UCard class="mt-4">
           <div class="space-y-4">
@@ -52,6 +56,11 @@ const tabs = [
     label: 'Tags',
     icon: 'i-heroicons-tag'
   },
+  {
+    key: 'app',
+    label: 'App',
+    icon: 'i-heroicons-device-phone-mobile'
+  },
   {
     key: 'account',
     label: 'Account',