feat(loyalty): transaction categories (what was sold)

Merchants can configure per-store product categories (e.g., Men,
Women, Accessories, Kids) that sellers select when entering loyalty
transactions. Enables per-category sales analytics.

Backend:
- New model: StoreTransactionCategory (store-scoped, max 10 per store)
- Migration loyalty_007: creates table + adds category_id FK on
  loyalty_transactions
- New category_service.py with CRUD + validation
- New schemas/category.py (Create, Update, Response, ListResponse)
- Admin CRUD: GET/POST/PATCH/DELETE /admin/loyalty/stores/{id}/categories
- Store CRUD: GET/POST/PATCH/DELETE /store/loyalty/categories
- Stamp/Points request schemas accept optional category_id
- Stamp/Points services pass category_id to transaction creation
- TransactionResponse includes category_id + category_name

342 tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/loyalty/schemas/points.py

@@ -47,6 +47,12 @@ class PointsEarnRequest(BaseModel):
         description="Staff PIN for verification",
     )
 
+    # Category (what was sold)
+    category_id: int | None = Field(
+        None,
+        description="Transaction category ID (e.g., Men, Women, Accessories)",
+    )
+
     # Optional metadata
     notes: str | None = Field(
         None,