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/reflector/pipelines/main_file_pipeline.py

@@ -87,15 +87,9 @@ class PipelineMainFile(PipelineMainBase):
         self.logger = logger.bind(transcript_id=self.transcript_id)
         self.empty_pipeline = EmptyPipeline(logger=self.logger)
 
-    async def get_transcript(self, session: AsyncSession = None) -> Transcript:
+    async def get_transcript(self, session: AsyncSession) -> Transcript:
         """Get transcript with session"""
-        if session:
-            result = await transcripts_controller.get_by_id(session, self.transcript_id)
-        else:
-            async with get_session_factory()() as session:
-                result = await transcripts_controller.get_by_id(
-                    session, self.transcript_id
-                )
+        result = await transcripts_controller.get_by_id(session, self.transcript_id)
         if not result:
             raise Exception("Transcript not found")
         return result