Meter tracks belong to their own meter (kw1e9)

Two leftovers from the sub-cell meter work.

The run detail's race bar was four cells with whole-cell rounding — five possible renderings, so a worker at 60% of the fastest and one at 70% drew exactly the same bar, in the view whose entire purpose is comparing worker speed. It now goes through the same shared sub-cell builder the progress meter uses, giving 33 distinguishable states in the same four columns.

Every empty track was also a shared neutral. Read out of the installed Claude Code binary, it carries a track pair per theme — and those are not two independent colours: every channel of the empty track is the fill scaled by 0.451. The track is a desaturated version of the FILL, in the same hue family. Each meter's track is now derived from its own fill by that rule, which holds across all five variants without adding a token per variant per meter. npm run selftest:tui-track-and-racebar reproduces the binary's own measured pair through the derivation as its anchor.

This supersedes the intermediate step in the sub-cell work, which had moved tracks onto the shared rule tone — better than the muted TEXT tone it replaced, but still a colour borrowed from another part of the system.

Known Limitations and Deferred Work. The 0.451 scale is measured from the binary's dark theme. The light-variant counterpart blends toward white by a symmetric amount and is NOT independently verified — Claude's light theme does not expose the pair. A fill that is a terminal-defined ANSI colour name has no numeric value to scale, so those variants fall back to the rule tone.