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_entry/routes.py

@@ -5,8 +5,8 @@ from sqlalchemy import select, update
 
 from models.calendars import CalendarEntry, CalendarSlot
 
-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 sqlalchemy import select
@@ -142,7 +142,7 @@ def register():
             calendars = (
                 await g.s.execute(
                     select(Calendar)
-                    .where(Calendar.post_id == post.id, Calendar.deleted_at.is_(None))
+                    .where(Calendar.container_type == "page", Calendar.container_id == post.id, Calendar.deleted_at.is_(None))
                     .order_by(Calendar.name.asc())
                 )
             ).scalars().all()
@@ -199,7 +199,7 @@ def register():
     @bp.get("/")
     @require_admin
     async def get(entry_id: int, **rest):
-        from suma_browser.app.utils.htmx import is_htmx_request
+        from shared.browser.app.utils.htmx import is_htmx_request
 
         # TODO: Create _main_panel.html and _oob_elements.html for optimized HTMX
         # For now, render full template for both HTMX and normal requests