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

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

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

bp/calendar_entry/services/post_associations.py

@@ -5,7 +5,7 @@ from sqlalchemy import select
 from sqlalchemy.sql import func
 
 from models.calendars import CalendarEntry, CalendarEntryPost
-from blog.models.ghost_content import Post
+from shared.models.ghost_content import Post
 
 
 async def add_post_to_entry(