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/ticket_admin/routes.py

@@ -18,8 +18,8 @@ from sqlalchemy import select, func
 from sqlalchemy.orm import selectinload
 
 from models.calendars import CalendarEntry, Ticket, TicketType
-from suma_browser.app.authz import require_admin
-from suma_browser.app.redis_cacher import clear_cache
+from shared.browser.app.authz import require_admin
+from shared.browser.app.redis_cacher import clear_cache
 
 from ..tickets.services.tickets import (
     get_ticket_by_code,
@@ -37,7 +37,7 @@ def register() -> Blueprint:
     @require_admin
     async def dashboard():
         """Ticket admin dashboard with QR scanner and recent tickets."""
-        from suma_browser.app.utils.htmx import is_htmx_request
+        from shared.browser.app.utils.htmx import is_htmx_request
 
         # Get recent tickets
         result = await g.s.execute(
@@ -89,7 +89,7 @@ def register() -> Blueprint:
     @require_admin
     async def entry_tickets(entry_id: int):
         """List all tickets for a specific calendar entry."""
-        from suma_browser.app.utils.htmx import is_htmx_request
+        from shared.browser.app.utils.htmx import is_htmx_request
 
         entry = await g.s.scalar(
             select(CalendarEntry)