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>

events/bp/calendars/services/calendars.py

@@ -6,7 +6,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from models.calendars import Calendar
 from shared.infrastructure.data_client import fetch_data
 from shared.contracts.dtos import PostDTO, dto_from_dict
-from shared.services.relationships import attach_child, detach_child
+from shared.infrastructure.actions import call_action
 import unicodedata
 import re
 
@@ -71,7 +71,10 @@ async def soft_delete(sess: AsyncSession, post_slug: str, calendar_slug: str) ->
 
     cal.deleted_at = utcnow()
     await sess.flush()
-    await detach_child(sess, "page", cal.container_id, "calendar", cal.id)
+    await call_action("cart", "detach-child", payload={
+        "parent_type": "page", "parent_id": cal.container_id,
+        "child_type": "calendar", "child_id": cal.id,
+    })
     return True
 
 async def create_calendar(sess: AsyncSession, post_id: int, name: str) -> Calendar:
@@ -105,14 +108,20 @@ async def create_calendar(sess: AsyncSession, post_id: int, name: str) -> Calend
         if existing.deleted_at is not None:
             existing.deleted_at = None  # revive
             await sess.flush()
-            await attach_child(sess, "page", post_id, "calendar", existing.id)
+            await call_action("cart", "attach-child", payload={
+                "parent_type": "page", "parent_id": post_id,
+                "child_type": "calendar", "child_id": existing.id,
+            })
             return existing
         raise CalendarError(f'Calendar with slug "{slug}" already exists for post {post_id}.')
 
     cal = Calendar(container_type="page", container_id=post_id, name=name, slug=slug)
     sess.add(cal)
     await sess.flush()
-    await attach_child(sess, "page", post_id, "calendar", cal.id)
+    await call_action("cart", "attach-child", payload={
+        "parent_type": "page", "parent_id": post_id,
+        "child_type": "calendar", "child_id": cal.id,
+    })
     return cal