refactor: improve session management across worker tasks and pipelines

- Remove "if session" anti-pattern from all functions
- Functions now require explicit AsyncSession parameters instead of optional session_factory
- Worker tasks (Celery) create sessions at top level using session_factory
- Add proper AsyncSession type annotations to all session parameters
- Update cleanup.py: delete_single_transcript, cleanup_old_transcripts, cleanup_old_public_data
- Update process.py: process_recording, process_meetings, reprocess_failed_recordings
- Update ics_sync.py: sync_room_ics, sync_all_ics_calendars, create_upcoming_meetings
- Update pipeline classes: get_transcript methods now require session
- Fix tests to pass sessions correctly

Benefits:
- Better type safety and IDE support with explicit AsyncSession typing
- Clear transaction boundaries with sessions created at task level
- Consistent session management pattern across codebase
- No ambiguity about session vs session_factory usage

server/tests/test_pipeline_main_file.py

@@ -624,7 +624,10 @@ async def test_pipeline_file_process_no_transcript():
 
         # Should raise an exception for missing transcript when get_transcript is called
         with pytest.raises(Exception, match="Transcript not found"):
-            await pipeline.get_transcript()
+            from reflector.db import get_session_factory
+
+            async with get_session_factory()() as session:
+                await pipeline.get_transcript(session)
 
 
 @pytest.mark.asyncio