feat: configure service worker and offline support (#34)

- Enhance Workbox configuration with comprehensive caching strategies
- Add separate caching for Supabase REST API, Storage, and Auth
- Configure Open Food Facts API caching (30-day cache)
- Add offline fallback page with retry functionality
- Create useOnlineStatus composable for network monitoring
- Add OfflineBanner component for user feedback
- Configure skipWaiting and clientsClaim for instant updates
- Cache Google Fonts and product images

Caching strategies:
- Network-first: Supabase REST API (fresh data priority)
- Network-only: Auth endpoints (never cache sensitive auth)
- Cache-first: Images, fonts, product data (performance)
- Offline fallback: /offline page for failed navigations

Closes #34

app/app/app.vue

@@ -1,5 +1,8 @@
 <template>
+  <div>
+    <OfflineBanner />
     <NuxtLayout>
       <NuxtPage />
     </NuxtLayout>
+  </div>
 </template>

app/components/OfflineBanner.vue

@@ -0,0 +1,58 @@
+<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="!isOnline"
+      class="fixed top-0 left-0 right-0 z-50 bg-amber-500 text-white px-4 py-2 text-center shadow-lg"
+    >
+      <div class="flex items-center justify-center gap-2">
+        <UIcon name="i-heroicons-wifi-slash" class="w-5 h-5" />
+        <span class="font-medium">
+          You're currently offline. Changes will sync when connection is restored.
+        </span>
+      </div>
+    </div>
+  </Transition>
+  
+  <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="isOnline && wasOffline && showReconnected"
+      class="fixed top-0 left-0 right-0 z-50 bg-emerald-500 text-white px-4 py-2 text-center shadow-lg"
+    >
+      <div class="flex items-center justify-center gap-2">
+        <UIcon name="i-heroicons-wifi" class="w-5 h-5" />
+        <span class="font-medium">
+          Back online! Syncing your changes...
+        </span>
+      </div>
+    </div>
+  </Transition>
+</template>
+
+<script setup lang="ts">
+const { isOnline, wasOffline } = useOnlineStatus()
+const showReconnected = ref(false)
+
+// Show "back online" message for 3 seconds
+watch(isOnline, (online) => {
+  if (online && wasOffline.value) {
+    showReconnected.value = true
+    setTimeout(() => {
+      showReconnected.value = false
+    }, 3000)
+  }
+})
+</script>

app/composables/useOnlineStatus.ts

@@ -0,0 +1,47 @@
+/**
+ * Composable to track online/offline status
+ * 
+ * Usage:
+ * const { isOnline, wasOffline } = useOnlineStatus()
+ * 
+ * watch(isOnline, (online) => {
+ *   if (online && wasOffline.value) {
+ *     // User came back online, sync data
+ *   }
+ * })
+ */
+export function useOnlineStatus() {
+  const isOnline = ref(true)
+  const wasOffline = ref(false)
+
+  if (process.client) {
+    // Initial state
+    isOnline.value = navigator.onLine
+
+    // Listen for online/offline events
+    const updateOnlineStatus = () => {
+      const online = navigator.onLine
+      
+      if (!online && isOnline.value) {
+        // Just went offline
+        wasOffline.value = true
+      }
+      
+      isOnline.value = online
+    }
+
+    window.addEventListener('online', updateOnlineStatus)
+    window.addEventListener('offline', updateOnlineStatus)
+
+    // Cleanup on unmount
+    onUnmounted(() => {
+      window.removeEventListener('online', updateOnlineStatus)
+      window.removeEventListener('offline', updateOnlineStatus)
+    })
+  }
+
+  return {
+    isOnline: readonly(isOnline),
+    wasOffline: readonly(wasOffline)
+  }
+}

app/nuxt.config.ts

@@ -77,37 +77,101 @@ export default defineNuxtConfig({
       ]
     },
     workbox: {
-      navigateFallback: '/',
-      globPatterns: ['**/*.{js,css,html,png,svg,ico}'],
+      navigateFallback: '/offline',
+      navigateFallbackDenylist: [/^\/api\//],
+      globPatterns: ['**/*.{js,css,html,png,svg,ico,woff,woff2}'],
       cleanupOutdatedCaches: true,
+      skipWaiting: true,
+      clientsClaim: true,
       runtimeCaching: [
+        // Supabase API - Network first with fallback
         {
-          urlPattern: /^https:\/\/api\.supabase\.co\/.*/i,
+          urlPattern: /^https:\/\/.*\.supabase\.co\/rest\/.*/i,
           handler: 'NetworkFirst',
           options: {
-            cacheName: 'supabase-api',
+            cacheName: 'supabase-rest-api',
+            networkTimeoutSeconds: 10,
             expiration: {
-              maxEntries: 100,
-              maxAgeSeconds: 60 * 60 * 24 // 24 hours
+              maxEntries: 50,
+              maxAgeSeconds: 60 * 60 // 1 hour
             },
             cacheableResponse: {
               statuses: [0, 200]
             }
           }
         },
+        // Supabase Auth - Network only (don't cache auth)
         {
-          urlPattern: /^https:\/\/.*\.supabase\.co\/.*/i,
-          handler: 'NetworkFirst',
+          urlPattern: /^https:\/\/.*\.supabase\.co\/auth\/.*/i,
+          handler: 'NetworkOnly'
+        },
+        // Supabase Storage - Cache first for images
+        {
+          urlPattern: /^https:\/\/.*\.supabase\.co\/storage\/.*/i,
+          handler: 'CacheFirst',
           options: {
-            cacheName: 'supabase-data',
+            cacheName: 'supabase-storage',
             expiration: {
               maxEntries: 100,
-              maxAgeSeconds: 60 * 60 * 24 // 24 hours
+              maxAgeSeconds: 60 * 60 * 24 * 7 // 1 week
             },
             cacheableResponse: {
               statuses: [0, 200]
             }
           }
+        },
+        // Open Food Facts API - Cache first with network fallback
+        {
+          urlPattern: /^https:\/\/world\.openfoodfacts\.org\/.*/i,
+          handler: 'CacheFirst',
+          options: {
+            cacheName: 'openfoodfacts-api',
+            expiration: {
+              maxEntries: 200,
+              maxAgeSeconds: 60 * 60 * 24 * 30 // 30 days
+            },
+            cacheableResponse: {
+              statuses: [0, 200]
+            }
+          }
+        },
+        // External images - Cache first
+        {
+          urlPattern: /^https:\/\/images\.openfoodfacts\.org\/.*/i,
+          handler: 'CacheFirst',
+          options: {
+            cacheName: 'product-images',
+            expiration: {
+              maxEntries: 100,
+              maxAgeSeconds: 60 * 60 * 24 * 30 // 30 days
+            },
+            cacheableResponse: {
+              statuses: [0, 200]
+            }
+          }
+        },
+        // Google Fonts - Cache first
+        {
+          urlPattern: /^https:\/\/fonts\.googleapis\.com\/.*/i,
+          handler: 'CacheFirst',
+          options: {
+            cacheName: 'google-fonts-stylesheets',
+            expiration: {
+              maxEntries: 20,
+              maxAgeSeconds: 60 * 60 * 24 * 365 // 1 year
+            }
+          }
+        },
+        {
+          urlPattern: /^https:\/\/fonts\.gstatic\.com\/.*/i,
+          handler: 'CacheFirst',
+          options: {
+            cacheName: 'google-fonts-webfonts',
+            expiration: {
+              maxEntries: 30,
+              maxAgeSeconds: 60 * 60 * 24 * 365 // 1 year
+            }
+          }
         }
       ]
     },

app/pages/offline.vue

@@ -0,0 +1,69 @@
+<template>
+  <div class="flex flex-col items-center justify-center min-h-screen p-8 text-center">
+    <UIcon name="i-heroicons-wifi-slash" class="w-24 h-24 text-gray-400 mb-6" />
+    
+    <h1 class="text-3xl font-bold text-gray-900 mb-4">
+      You're Offline
+    </h1>
+    
+    <p class="text-gray-600 mb-8 max-w-md">
+      No internet connection detected. Some features may be limited, but you can still:
+    </p>
+    
+    <div class="space-y-3 mb-8 text-left max-w-md">
+      <div class="flex items-start gap-3">
+        <UIcon name="i-heroicons-check-circle" class="w-6 h-6 text-emerald-500 mt-0.5" />
+        <span class="text-gray-700">View cached inventory items</span>
+      </div>
+      <div class="flex items-start gap-3">
+        <UIcon name="i-heroicons-check-circle" class="w-6 h-6 text-emerald-500 mt-0.5" />
+        <span class="text-gray-700">Scan barcodes (will sync when online)</span>
+      </div>
+      <div class="flex items-start gap-3">
+        <UIcon name="i-heroicons-check-circle" class="w-6 h-6 text-emerald-500 mt-0.5" />
+        <span class="text-gray-700">Browse previously loaded data</span>
+      </div>
+    </div>
+    
+    <UButton
+      color="emerald"
+      size="lg"
+      @click="retry"
+      :loading="retrying"
+    >
+      <template #leading>
+        <UIcon name="i-heroicons-arrow-path" />
+      </template>
+      Try Again
+    </UButton>
+  </div>
+</template>
+
+<script setup lang="ts">
+const retrying = ref(false)
+
+async function retry() {
+  retrying.value = true
+  
+  try {
+    // Test if we're back online
+    const response = await fetch('/api/health', { method: 'HEAD' })
+    if (response.ok) {
+      // We're online! Go back
+      window.location.reload()
+    }
+  } catch (error) {
+    // Still offline
+    setTimeout(() => {
+      retrying.value = false
+    }, 1000)
+  }
+}
+
+// Auto-retry when online event fires
+if (typeof window !== 'undefined') {
+  window.addEventListener('online', () => {
+    window.location.reload()
+  })
+}
+</script>