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/pages/index.vue

@@ -17,36 +17,37 @@
           color="white" 
           size="lg"
           icon="i-heroicons-plus"
+          @click="showAddForm = true"
         >
           Add Manually
         </UButton>
       </div>
     </div>
 
-    <!-- Empty State -->
-    <UCard v-if="true">
-      <div class="text-center py-12">
-        <UIcon 
-          name="i-heroicons-inbox" 
-          class="w-16 h-16 text-gray-400 mx-auto mb-4"
+    <!-- Add Item Form (Overlay) -->
+    <div v-if="showAddForm" class="fixed inset-0 z-50 flex items-start justify-center pt-20 px-4 bg-black/50">
+      <div class="w-full max-w-lg">
+        <AddItemForm 
+          @close="showAddForm = false"
+          @added="handleItemAdded"
         />
-        <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>
-        <UButton 
-          to="/scan" 
-          color="primary"
-          icon="i-heroicons-qr-code"
-        >
-          Scan First Item
-        </UButton>
       </div>
-    </UCard>
+    </div>
 
-    <!-- TODO: Item list will go here -->
+    <!-- Edit Item Modal -->
+    <EditItemModal 
+      :item="editingItem"
+      @close="editingItem = null"
+      @updated="handleItemUpdated"
+    />
+
+    <!-- Inventory List -->
+    <InventoryList
+      ref="inventoryListRef"
+      :refresh="refreshKey"
+      @add-item="showAddForm = true"
+      @edit-item="editingItem = $event"
+    />
   </div>
 </template>
 
@@ -54,4 +55,20 @@
 definePageMeta({
   layout: 'default'
 })
+
+const showAddForm = ref(false)
+const editingItem = ref<any>(null)
+const refreshKey = ref(0)
+const inventoryListRef = ref()
+
+const handleItemAdded = (item: any) => {
+  showAddForm.value = false
+  // Reload the inventory list
+  inventoryListRef.value?.reload()
+}
+
+const handleItemUpdated = (item: any) => {
+  editingItem.value = null
+  inventoryListRef.value?.reload()
+}
 </script>