- Rewrite LibraryCache from JSON (cache dir) to SQLite (data dir with WAL)
- Each track gets a stable UUID so play stats survive file renames/re-encodes
- Thread-safe via PRAGMA busy_timeout + RLock
- Automatic backup rotation (.backup, .bak) on every write
- One-shot migration from old ~/.cache/library_cache.json
- Add SessionStore (~/.local/share/session.json) for playback state
- Add SplashOverlay with spinning animation on first (empty-DB) launch
- _scan_library() now accepts on_progress callback for the overlay
- Fix _mtime → mtime SQLite column name lookup in recently-added filter
- PlaylistManager path migrated to ~/.local/share/ with auto-migration
- Metadata sync: remove dead consume_play_deltas(), use library API
