feat(loyalty): multi-select categories on transactions

Switch from single category_id to category_ids JSON array on
transactions. Sellers can now select multiple categories (e.g.,
Men + Accessories) when entering stamp/points transactions.

- Migration loyalty_009: drop category_id FK, add category_ids JSON
- Schemas: category_id → category_ids (list[int] | None)
- Services: stamp_service + points_service accept category_ids
- Terminal UI: pills are now multi-select (toggle on/off)
- Transaction response: category_names (list[str]) resolved from IDs
- Recent transactions table: new Category column showing comma-
  separated names

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

app/modules/loyalty/services/points_service.py

@@ -49,7 +49,7 @@ class PointsService:
         purchase_amount_cents: int,
         order_reference: str | None = None,
         staff_pin: str | None = None,
-        category_id: int | None = None,
+        category_ids: list[int] | None = None,
         ip_address: str | None = None,
         user_agent: str | None = None,
         notes: str | None = None,
@@ -104,7 +104,7 @@ class PointsService:
             raise OrderReferenceRequiredException()
 
         # Category is mandatory when the store has categories configured
-        if not category_id:
+        if not category_ids:
             from app.modules.loyalty.services.category_service import category_service
 
             store_categories = category_service.list_categories(
@@ -196,7 +196,7 @@ class PointsService:
             card_id=card.id,
             store_id=store_id,
             staff_pin_id=verified_pin.id if verified_pin else None,
-            category_id=category_id,
+            category_ids=category_ids,
             transaction_type=TransactionType.POINTS_EARNED.value,
             points_delta=points_earned,
             stamps_balance_after=card.stamp_count,