Decouple blog: use shared.models for all cross-app imports

- Replace all imports from cart.models, market.models, events.models
  with shared.models equivalents
- Convert blog/models/ghost_content.py to re-export stub
- Update shared + glue submodule pointers

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

bp/post/services/entry_associations.py

@@ -4,7 +4,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy import select
 from sqlalchemy.sql import func
 
-from events.models.calendars import CalendarEntry, CalendarEntryPost, Calendar
+from shared.models.calendars import CalendarEntry, CalendarEntryPost, Calendar
 from models.ghost_content import Post
 
 

bp/post/services/markets.py

@@ -6,9 +6,9 @@ import unicodedata
 from sqlalchemy import select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from market.models.market_place import MarketPlace
+from shared.models.market_place import MarketPlace
 from models.ghost_content import Post
-from cart.models.page_config import PageConfig
+from shared.models.page_config import PageConfig
 from shared.browser.app.utils import utcnow
 from glue.services.relationships import attach_child, detach_child