Move container_relations to cart service for cross-service ownership

container_relations is a generic parent/child graph used by blog
(menu_nodes), market (marketplaces), and events (calendars). Move it
to cart as shared infrastructure. All services now call cart actions
(attach-child/detach-child) instead of querying the table directly.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

shared/services/market_impl.py

@@ -12,7 +12,7 @@ from shared.models.market import Product
 from shared.models.market_place import MarketPlace
 from shared.browser.app.utils import utcnow
 from shared.contracts.dtos import MarketPlaceDTO, ProductDTO
-from shared.services.relationships import attach_child, detach_child
+from shared.infrastructure.actions import call_action
 
 
 def _mp_to_dto(mp: MarketPlace) -> MarketPlaceDTO:
@@ -93,7 +93,10 @@ class SqlMarketService:
                 existing.deleted_at = None  # revive
                 existing.name = name
                 await session.flush()
-                await attach_child(session, container_type, container_id, "market", existing.id)
+                await call_action("cart", "attach-child", payload={
+                    "parent_type": container_type, "parent_id": container_id,
+                    "child_type": "market", "child_id": existing.id,
+                })
                 return _mp_to_dto(existing)
             raise ValueError(f'Market with slug "{slug}" already exists for this container.')
 
@@ -103,7 +106,10 @@ class SqlMarketService:
         )
         session.add(market)
         await session.flush()
-        await attach_child(session, container_type, container_id, "market", market.id)
+        await call_action("cart", "attach-child", payload={
+            "parent_type": container_type, "parent_id": container_id,
+            "child_type": "market", "child_id": market.id,
+        })
         return _mp_to_dto(market)
 
     async def soft_delete_marketplace(
@@ -124,5 +130,8 @@ class SqlMarketService:
 
         market.deleted_at = utcnow()
         await session.flush()
-        await detach_child(session, container_type, container_id, "market", market.id)
+        await call_action("cart", "detach-child", payload={
+            "parent_type": container_type, "parent_id": container_id,
+            "child_type": "market", "child_id": market.id,
+        })
         return True