feat: implement inventory CRUD UI components (#18 #19 #20 #21)

Week 2 core inventory management:

**Composables:**
- useInventory: Full CRUD operations for inventory items
- useUnits: Unit fetching and conversion helpers
- useTags: Tag fetching and category filtering

**Components:**
- InventoryList (#18): Grid view with loading/empty/error states
- InventoryCard: Item card with image, quantity controls, tags, expiry
- AddItemForm (#19): Form with tag picker, unit selector, validation
- EditItemModal (#20): Modal form for editing existing items
- Delete functionality (#21): Confirm dialog + cascade tag cleanup

**Features:**
- Quantity quick-actions (+/- buttons on cards)
- Auto-delete when quantity reaches zero
- Expiry date tracking with color-coded warnings
- Tag selection by category in add form
- Responsive grid layout (1-4 columns)
- Product image display from barcode cache
- Form validation and loading states

Closes #18, #19, #20, #21

app/components/inventory/InventoryList.vue

@@ -0,0 +1,131 @@
+<template>
+  <div class="space-y-4">
+    <!-- Loading State -->
+    <div v-if="loading" class="text-center py-12">
+      <UIcon name="i-heroicons-arrow-path" class="w-8 h-8 text-gray-400 animate-spin mx-auto mb-2" />
+      <p class="text-gray-600">Loading inventory...</p>
+    </div>
+
+    <!-- Error State -->
+    <div v-else-if="error" class="text-center py-12">
+      <UIcon name="i-heroicons-exclamation-triangle" class="w-12 h-12 text-red-500 mx-auto mb-4" />
+      <p class="text-red-600 mb-4">{{ error }}</p>
+      <UButton @click="loadInventory" color="gray">Retry</UButton>
+    </div>
+
+    <!-- Empty State -->
+    <div v-else-if="!items || items.length === 0" class="text-center py-12">
+      <UIcon name="i-heroicons-inbox" class="w-16 h-16 text-gray-400 mx-auto mb-4" />
+      <h3 class="text-lg font-semibold text-gray-900 mb-2">
+        No items yet
+      </h3>
+      <p class="text-gray-600 mb-6">
+        Start by scanning a barcode or adding an item manually.
+      </p>
+      <div class="flex gap-2 justify-center">
+        <UButton 
+          to="/scan" 
+          color="primary"
+          icon="i-heroicons-qr-code"
+        >
+          Scan First Item
+        </UButton>
+        <UButton 
+          @click="$emit('add-item')"
+          color="white"
+          icon="i-heroicons-plus"
+        >
+          Add Manually
+        </UButton>
+      </div>
+    </div>
+
+    <!-- Inventory Grid -->
+    <div v-else class="grid gap-4 sm:grid-cols-2 lg:grid-cols-3 xl:grid-cols-4">
+      <InventoryCard
+        v-for="item in items"
+        :key="item.id"
+        :item="item"
+        @edit="$emit('edit-item', item)"
+        @delete="handleDelete(item.id)"
+        @update-quantity="handleQuantityUpdate"
+      />
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+const { getInventory, deleteInventoryItem, updateQuantity } = useInventory()
+
+const props = defineProps<{
+  refresh?: boolean
+}>()
+
+const emit = defineEmits<{
+  'add-item': []
+  'edit-item': [item: any]
+}>()
+
+const items = ref<any[]>([])
+const loading = ref(true)
+const error = ref<string | null>(null)
+
+const loadInventory = async () => {
+  loading.value = true
+  error.value = null
+
+  const { data, error: fetchError } = await getInventory()
+
+  if (fetchError) {
+    error.value = 'Failed to load inventory. Please try again.'
+    loading.value = false
+    return
+  }
+
+  items.value = data || []
+  loading.value = false
+}
+
+const handleDelete = async (id: string) => {
+  if (!confirm('Are you sure you want to delete this item?')) {
+    return
+  }
+
+  const { error: deleteError } = await deleteInventoryItem(id)
+
+  if (deleteError) {
+    alert('Failed to delete item')
+    return
+  }
+
+  // Remove from local list
+  items.value = items.value.filter(item => item.id !== id)
+}
+
+const handleQuantityUpdate = async (id: string, change: number) => {
+  const result = await updateQuantity(id, change)
+
+  if (result.error) {
+    alert('Failed to update quantity')
+    return
+  }
+
+  // Reload inventory after update
+  await loadInventory()
+}
+
+// Load on mount
+onMounted(loadInventory)
+
+// Watch for refresh prop
+watch(() => props.refresh, (newVal) => {
+  if (newVal) {
+    loadInventory()
+  }
+})
+
+// Expose reload method
+defineExpose({
+  reload: loadInventory
+})
+</script>