Find & Add was being forgotten on the next auto-sync. It persists two ways — a fast
sync_match_cache override AND a durable manual_library_match (#787) that survives a
rescan — but BOTH sync matchers (services.sync_service._find_track_in_media_server and
the DB-only fallback) only consulted the volatile cache. A library rescan wipes that
cache, so the next 'replace' auto-sync re-matched the track from scratch and the user
had to Find & Add it again.
Both matchers now fall back to the durable manual match when the cache misses
(self-healing a stale library id via the stored file path), exactly like the compare
view already does via resolve_durable_match_server_id. So a Find & Add pairing sticks
across rescans + auto-syncs. Seam tests: cache-wiped→durable hit, stale-id self-heal,
no-match→fuzzy fall-through.
cf2b4d7d38