feat(library): remove a track from the library without deleting the file

RemoveFromLibrary deletes the audio_files rows the way the scan's own
orphan cleanup does and records each path in excluded_paths. The
exclusion is not an enhancement: without it the next scan finds the
file, sees no row and imports it again, so the button undoes itself.

The soft scan compares files on disk against rows in the database, so
surveyAudioFiles and countAudioFiles both take the exclusion set —
otherwise an excluded path makes the two disagree forever and queues a
full scan on every launch. Deleting a row cascades to queue_tracks, so
the removal calls the same CompactQueue hook RemoveLibrary does.

Also lands the requested badge: library-status-indicator is a button
again where it can act, utils/library-status.ts states once what owning
and wanting mean, and the long-declared queued state finally has a
producer.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UDCbcCZQepnpSQYJ6SxxZm

backend/database/sql/queries/audio_files.sql

@@ -343,3 +343,7 @@ JOIN audio_files af ON af.recording_id = r.id
 WHERE r.mbid IN (sqlc.slice('mbids'))
   AND af.library_id = ?
 ORDER BY af.file_path;
+
+-- name: GetAudioFilesByPaths :many
+SELECT id, library_id, file_path, group_key FROM audio_files
+WHERE file_path IN (sqlc.slice('paths'));