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
