Restore global menu bar chrome to capture metrics

[baseGame]

Summary

• Verify stacked .menu-bar remains 48px (24px title + 24px menus) vs capture title22.5 + menu23.5 CSS (DPR≈2).
• Paint title band #f0f0f0 (capture) with white menu row; restore dropdown command rows to 22px / 12px (was 20px / 11px).
• Mark data-menu-density="capture-1to1"; keep Session/View/Tools/Help (and session-specific) labels.

Test plan

• Vitest shellChromeDensity, AppLayout.test.ts, full src/styles/
• Pre-commit quality (prettier, eslint, stylelint, vue-tsc, rust fmt/clippy)
• Spot-check vs docs/assets/.../home.png, folder-compare.png, text-compare.png (e2e still expects .menu-bar height 48px)

Remaining divergences

• Window title uses product name OpenDiff (capture shows vendor app name).
• Lucide brand glyph vs native system-menu icon.
• Menu contents / enablement depth intentionally out of scope; Options / Tol panels out of scope.