feat: MusicBrainz-aware intake and completeness check against canonical track count

worker/lyra_worker/resolver.py

@@ -0,0 +1,9 @@
+from typing import Protocol
+
+from lyra_worker.types import MBTarget
+
+
+class MbResolver(Protocol):
+    def resolve(self, artist: str, album: str) -> MBTarget | None:
+        """Return a canonical MBTarget (with track_count) or None if no confident match."""
+        ...