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/services/card_service.py

@@ -836,6 +836,8 @@ class CardService:
                 "transaction_at": tx.transaction_at.isoformat() if tx.transaction_at else None,
                 "notes": tx.notes,
                 "store_name": None,
+                "category_id": tx.category_id,
+                "category_name": None,
             }
 
             if tx.store_id:
@@ -843,6 +845,16 @@ class CardService:
                 if store_obj:
                     tx_data["store_name"] = store_obj.name
 
+            if tx.category_id:
+                from app.modules.loyalty.services.category_service import (
+                    category_service,
+                )
+
+                cat_name = category_service.validate_category_for_store(
+                    db, tx.category_id, tx.store_id or 0
+                )
+                tx_data["category_name"] = cat_name
+
             tx_responses.append(tx_data)
 
         return tx_responses, total