#21702 fix(cmux-next): reasoning menu check on the right

Summary

The reasoning menu (Reasoning: Low / Medium / High / Extra High / Max) kept an empty check column in front of every level, so each label and the section title sat indented. The check now marks the chosen row at its trailing edge, as Claude's model list does, and labels and the title start at the row's own inset. The highlight on the chosen row is unchanged.

Testing

• test/reasoning-menu-check.test.ts (new, Chromium and WebKit): the chosen row's check sits after its label within 12 px of the row's end; every label starts at the same inset with no gutter; the section title lines up with them. Committed before the fix. Not run locally (cosmic-gray load ~300 timed out Vite warm-up); CI's browser lane runs it. Checked by eye in headless WebKit on the gallery stage, before/after below.
• vp fmt --check and vp lint clean.

Changelog

Changed: The reasoning menu shows the selected level's check on the right instead of indenting every level

Proof

Headless WebKit on the gallery stage agent-pane.new-tab / reasoning-chip, dark, 2x.

🤖 Generated with Claude Code