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.

docs/api/inventory.md

@@ -31,6 +31,7 @@ List the tenant's items plus the four derived stat counters.
         "uuid": "…",
         "name": "دستکش جراحی",
         "consumable": "جراحی",
+        "category": "لوازم مصرفی و تزریقات",
         "unit": "عدد",
         "price": 250000,
         "stock": 150,
@@ -45,11 +46,29 @@ List the tenant's items plus the four derived stat counters.
 
 ### GET `/api/v1/inventory-categories`
 
-Distinct non-empty `consumable` values for the tenant — powers the filter dropdown.
+Distinct non-empty `category` values **actually in use** by the tenant — powers the
+filter dropdown. For the full list of allowed categories use `inventory-meta`.
 
 #### Response `200`
 ```json
-{ "success": true, "data": ["جراحی", "دندانپزشکی"] }
+{ "success": true, "data": ["دارو", "لوازم آزمایشگاهی"] }
+```
+
+### GET `/api/v1/inventory-meta`
+
+Backend-owned option lists for the item form. **Single source of truth** — the
+admin never hardcodes units/categories. Values are plain Persian strings stored
+as-is; the create/update endpoints validate against these lists.
+
+#### Response `200`
+```json
+{
+  "success": true,
+  "data": {
+    "units": ["عدد", "بسته", "…", "سی‌سی", "میلی‌لیتر", "…"],
+    "categories": ["دارو", "لوازم مصرفی و تزریقات", "…", "سایر"]
+  }
+}
 ```
 
 ### POST `/api/v1/inventory-item`
@@ -60,8 +79,9 @@ Create an item.
 | Field | Type | Required | Notes |
 |-------|------|----------|-------|
 | `name` | string | ✅ | نام کالا |
-| `consumable` | string | ❌ | «مصرفی» / گروه فیلتر |
-| `unit` | string | ❌ | Default `عدد` |
+| `consumable` | string | ❌ | «مصرفی» — یادداشت آزاد (سازگاری عقب‌رو) |
+| `category` | string | ❌ | دسته‌بندی؛ باید یکی از `inventory-meta.categories` باشد. خالی → `null`. فرم ادمین آن را الزامی می‌کند |
+| `unit` | string | ❌ | باید یکی از `inventory-meta.units` باشد. خالی → پیش‌فرض `عدد` |
 | `price` | integer | ❌ | Rial, Default `0` |
 | `stock` | integer | ❌ | Default `0` |
 | `alertThreshold` | integer | ❌ | Default `0` |
@@ -74,7 +94,9 @@ Create an item.
 #### Errors
 | Status | Code | Cause |
 |--------|------|-------|
-| `422` | `ERR_VALIDATION_001` | `name` خالی است |
+| `422` | `ERR_VALIDATION_001` | `name` خالی است (field `name`) |
+| `422` | `ERR_VALIDATION_001` | `unit` خارج از لیست مجاز (field `unit`) |
+| `422` | `ERR_VALIDATION_001` | `category` خارج از لیست مجاز (field `category`) |
 | `403` | `ERR_FORBIDDEN_001` | پروفایل tenant یافت نشد |
 
 ### PATCH `/api/v1/inventory-item/{uuid}`