positionMs changes every poll (~20s), so the old live progress bar/elapsed
time forced a full flash constantly, even mid-song -- this panel has no
partial refresh, so there's no way to show real progress without that.
Now it's an outline + total length only, driven by nothing that changes
while the same track keeps playing. Verified the rendered image is
byte-identical across different positionMs values for the same track.
Also dropped elapsed/elapsed_text/progress_pct from the track dict
entirely now that nothing renders them.