feat(library): Reanalyze and Remove-from-library context menu

[robmorgan]

Summary

Right-clicking a track row in the library browser (now anywhere on the row, not just the Title cell) offers two new actions below the playlist items:

• Reanalyze — clears analysis_json (new Library::clear_analysis), which re-arms the worker's next_unanalyzed queue, and wakes the analysis worker for an immediate run. The BPM column stays populated while the worker re-runs. The Analyzed event handler no longer skips decks that already hold an artifact, so a loaded deck picks up the refreshed grid (the engine-side apply still waits for a non-playing moment via pending_artifact).
• Remove from library… — opens a centered confirmation dialog ("Authored lighting cues will be deleted. The audio file on disk is not touched.") since the FK cascade drops playlist_tracks and lighting_cues. On confirm, Library::delete_track deletes the row, any deck/audition still holding the track is detached (track_id = None) without interrupting playback, and the status bar reports the removal.

Testing

• 2 new library unit tests: clear_analysis re-arms the queue (including from the '' failure marker), and delete_track cascades playlist membership + lighting cues while the playlist itself survives. cargo test --workspace: 119 passed.
• Manual: right-clicked the row → menu shows Add to playlist / Reanalyze / Remove from library…; Reanalyze produced a second "Analyzed" log line; Remove showed the dialog, Cancel kept the row, Remove emptied the library ("0 tracks", status message) while deck A kept playing its loaded track. No underruns/errors in the log.

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