Closes the gap from cf2b4d7d: that commit unit-tested the DB-only matcher twin but
not services.sync_service._find_track_in_media_server — the actual path a connected
Plex/Jellyfin user hits. Drive it directly (Jellyfin server-type, so no Plex fetchItem
mocking): durable manual match is honored when the volatile cache is wiped, and a
stale library id self-heals via the stored file path.
