- Add FallbackController for proper 404 JSON responses on missing resources
- Add non-bang get_source/1 and get_media_item/1 for safe lookups
- Fix Task JSON encoder: remove Repo.preload call (not available in encoder scope),
handle NotLoaded associations by returning nil
- Fix media item index: use list_media_items_for_source/1 instead of
list_pending_media_items_for/1 which had overly restrictive filtering
- Add missing extras_directory to test config
- All 1007 tests pass
