role_detector: classify items as Interstitial by collection name/tag patterns.
Wire chapter extraction + role detection into sync adapter (worker + presentation).
SQLite: persist/read role column, migration.
PUT /library/items/{id}/role endpoint for manual override.
Move auto_scheduler, library_sync, broadcast_poller, webhook_consumer
from presentation/background/ into crates/worker/src/jobs/.
Presentation is now a pure HTTP server.
