feat(music): show station and track names, not stream URLs (fancy UI phase 1)

The EMMS playlist showed the raw stream URL for every radio track, so the buffer read like a debug log. This is phase 1 of the fancy player: real names, still plain text. It ships on its own and becomes the fallback for the image and GUI phases.

I split the old cj/music--track-description into a pure, name-only cj/music--display-name that the header's Current line and the row renderer both call, so the two never drift. A url track resolves to its #EXTINF label (read once from all the playlist .m3u files into a cached map) or a tidied host. A file shows Artist - Title or its filename. The row renderer adds a dim nerd-icon glyph and the duration as right-aligned meta with an :align-to space, so it survives a window resize. The header line stays clean: just the name plus an on-air or duration suffix.

The pure helpers carry the tests: display-name, tidy-host, m3u-labels, bar-fill, format-meta, Normal/Boundary/Error each (32 tests across four files). The glyph, the aligned meta, and the disk-backed name map are the thin composition, verified live against 44 real stations.

The progress bar's visual and its live elapsed source come in phase 3. The bar-fill helper is the tested pure core it will feed. The full suite is green.

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