feat: decouple events from shared_lib, add app-owned models

Phase 1-3 of decoupling:
- path_setup.py adds project root to sys.path
- Events-owned models in events/models/ (calendars with all related models)
- All imports updated: shared.infrastructure, shared.db, shared.browser, etc.
- Calendar uses container_type/container_id instead of post_id FK
- CalendarEntryPost uses content_type/content_id (generic content refs)

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

bp/calendar/services/adopt_session_entries_for_user.py

@@ -1,5 +1,6 @@
 from sqlalchemy import select, update
 from models.calendars import CalendarEntry
+
 from sqlalchemy import func
 
 async def adopt_session_entries_for_user(session, user_id: int, session_id: str | None) -> None: