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/slots/services/slots.py

@@ -8,6 +8,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 
 from models.calendars import CalendarSlot
 
+
 class SlotError(ValueError):
     pass