Terminal: resolve the ANSI palette per appearance

[neo773]

The dynamic light/dark switch themed the terminal's chrome but not its grid. The panel read Theme, while the cells painted from two constants: a hardcoded #090909 background and a single ANSI table tuned by eye against it.

In light mode that renders a near-black rectangle inside a white app, and the "bright" half of the palette — the half most CLI output reaches for — comes out pale-on-pale.

What changed

crates/ui/src/terminal/view.rs. The background and the 16 named ANSI slots now resolve through Appearance:

• Background — #090909 dark, #fafafa light. The light step is larger than dark's 3/255 for the same reason Theme::light's surfaces are: a delta that reads as separation on near-black disappears on white.
• ANSI 0–15 — a second table, same hue families walked down to the 600/700 steps, the way Theme::light already does for its accents. "Bright" keeps meaning more prominent, which on a light field is darker. A literal copy of the dark table would have made the bright half the invisible half.
• The 6×6×6 cube (16–231) — deliberately left appearance-independent. A program asking for index 196 is asking for #ff0000 by arithmetic; remapping it would invent colors nobody picked. iTerm and Apple Terminal light themes do the same.
• The grayscale ramp (232–255) — mirrored. Tools use it for de-emphasis rather than for a specific grey, and its bright end (where dim hint text lands) is the end that vanishes on white.

One real finding while writing the tests: light yellow at yellow-600 measures 2.81:1 on the light background and misses AA. It moved to amber-700 — the step Theme::light already picked for its own warning token, for the same reason.

Tests

Five new, in the same module:

• a per-slot contrast floor against each palette's own background — the check that would have caught the original omission
• bright-is-more-prominent, asserted in both directions
• the grayscale ramp mirrors; the cube does not
• the palette tables actually differ

Both contrast tests carry the black / bright-black pair as a documented exception rather than skipping it silently: those are structural greys, and the shipped dark tuning puts bright-black at 2.58:1.

comet-ui is 362/362 green, clippy and fmt clean. Verified by eye in the running app in both appearances and across a live switch.

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[wingleeio]

Reviewed the diff and verified locally: single-file UI change (color tables + tests), no I/O/unsafe/dependency changes. Merged onto current main: 362/362 tests pass, fmt clean, zero clippy warnings in the changed file. Cube indices stay appearance-independent as described; grayscale mirror is exact. Safe to merge.