feat(node): recognize WMA and Musepack as audio, read their real tag keys

A real-library scan turned up 250 .wma and 23 .mpc files that the indexer
was silently classifying as "other" — genuinely lost from the Music app,
not a consolidation-rule artifact (checked separately: the grouping logic
itself drops nothing). Both are now indexed as audio and tagged properly:

- WMA has no mutagen "easy" wrapper, so the generic tag reader was reading
  nothing from it at all. Reads the real ASF keys directly instead
  (Title/Author/WM-AlbumTitle/WM-TrackNumber), confirmed against a real
  sample file before writing the mapping.
- Musepack's format auto-detection is unreliable enough (misidentified a
  real .mpc as MP3 in spot checks) that it now always opens by its own
  class instead of guessing from content.
- Filters out another placeholder value found along the way: a French
  ripping tool's auto-generated "Album inconnu (<timestamp>)".

Neither format decodes natively in a browser's <audio> element, so this
gets them correctly visible, tagged, and covered — not yet playable
in-browser. That would need server-side transcoding, deliberately left
out of this change.

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