feat(enrichment): record status/errors and trust high-confidence AcoustID

Two related gaps surfaced from "uploaded a track, nothing changed / no status":

- A track could stay stuck on `pending` forever (an unexpected worker error
  rolled back the run without recording anything), and `failed` carried no
  reason. Add `tracks.metadata_error` + `tracks.enriched_at` (migration), stamp
  the outcome in apply_enrichment, add TrackRepository.mark_enrichment_failed,
  wrap enrich_task to persist crashes as `failed` in a fresh session, and emit a
  human-readable no-match reason. Expose metadata_error/enriched_at in TrackOut.

- The tag-first merge let junk embedded tags (e.g. "Music Track"/"Sound_13958")
  override even a 0.99-confidence AcoustID match. Add acoustid_trust_score
  (default 0.85): above it the acoustic identity wins for title/artist/album/
  year, tags are fallback; below it, tag-first as before.

Add a license-free real-file fixture (Scarlet Fire / Otis McDonald) whose junk
tags AcoustID overrides, with an always-on tag-reader test plus fpcalc/AcoustID/
network-gated identity + full-pipeline tests (skip on host, run in the container).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_import_service.py

@@ -52,6 +52,8 @@ class FakeTrackRepo:
             genre=None,
             year=None,
             metadata_status=str(kw["metadata_status"]),
+            metadata_error=None,
+            enriched_at=None,
             created_at=now,
             updated_at=now,
         )
@@ -133,6 +135,8 @@ async def test_dedup_skips_already_imported() -> None:
         genre=None,
         year=None,
         metadata_status="pending",
+        metadata_error=None,
+        enriched_at=None,
         created_at=now,
         updated_at=now,
     )