Decoupling audit cleanup: fix protocol gaps, remove dead APIs

- Add search_posts, entry_ids_for_content, visible_entries_for_period
  to protocols and stubs
- Delete internal_api.py and factory cleanup hook (zero callers)
- Convert utils.py to utils/ package with calendar_helpers module
- Remove deleted_at check from calendar_view template (service filters)

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

infrastructure/factory.py

@@ -143,12 +143,6 @@ def create_base_app(
         async def _inject_base():
             return await base_context()
 
-    # --- cleanup internal API client on shutdown ---
-    @app.after_serving
-    async def _close_internal_client():
-        from .internal_api import close_client
-        await close_client()
-
     # --- event processor ---
     _event_processor = EventProcessor()