feat: Implement category and unit selection for inventory items

- Added a new 'category' field to the InventoryItem entity and updated the database schema.
- Replaced free-text input for 'unit' and 'category' with select dropdowns in the AddItemModal.
- Introduced a new API endpoint to fetch metadata for units and categories.
- Updated inventory filtering logic to use the new 'category' field instead of 'consumable'.
- Enhanced validation for item creation and updates to ensure valid unit and category values.
- Updated tests to cover new functionality and ensure proper validation.

assets/admin/pages/InventoryPage.tsx

@@ -14,7 +14,7 @@ type Tab = 'stock' | 'packages';
 /** انبارداری — consumable stock items + packages. Ported from clinic-pro-tauri /inventory. */
 export default function InventoryPage() {
   const {
-    items, stats, packages, categories, itemsLoading, packagesLoading,
+    items, stats, packages, categories, meta, itemsLoading, packagesLoading,
     createItem, updateItem, deleteItem, createPackage, updatePackage, deletePackage,
   } = useInventory();
 
@@ -31,7 +31,7 @@ export default function InventoryPage() {
     const q = search.trim();
     return items.filter((it) =>
       (q === '' || it.name.includes(q)) &&
-      (category === '' || it.consumable === category)
+      (category === '' || it.category === category)
     );
   }, [items, search, category]);
 
@@ -120,6 +120,7 @@ export default function InventoryPage() {
       <AddItemModal
         open={itemModal.open}
         editing={itemModal.editing}
+        meta={meta}
         saving={createItem.isPending || updateItem.isPending}
         onClose={() => setItemModal({ open: false, editing: null })}
         onSave={saveItem}