feat: state platform metrics and chrome in theme

docs/platform-metrics-audit.md

@@ -229,6 +229,10 @@ density is frozen at a macOS-ish tuning.
 
 ## Recommended changes, in priority order
 
+Landed 2026-11 with two deviations: Omarchy is grouped with GNOME (it
+styles its apps with adwaita), and macOS's titlebar is stated at the
+measured 32pt rather than queried at runtime (28pt on older builds).
+
 1. **State `control_height` per platform** — add `control_height:
    Option<Pixels>` beside `input_height` on `SystemTheme`, reuse the
    ratio-scaling pattern: macOS 24 (measured), Windows 32, GNOME ≈34, KDE
@@ -248,9 +252,11 @@ density is frozen at a macOS-ish tuning.
    queried rather than a drifted floor (32 on current builds, 28 older);
    Windows stays stated.
 6. **Add a minimal spacing scale to `Theme`** driven by a per-platform base
-   unit (GNOME 6, KDE 4/6/8, others 4); route menu/popover paddings, menu
-   item min-height (GNOME 32), and the hardcoded `min_w_`/`max_w` values
-   through it.
+   unit (GNOME 6, KDE 4/6/8, others 4); route menu/popover paddings and menu
+   row min-heights through it — GNOME 32 (published), Windows ≈33 (padding
+   4/5 + a 20px Body line + 2px item margins), KDE ≈29 (max(font, 20px
+   floors) + 1 + 2×4); the hardcoded `min_w_`/`max_w` surface values stay
+   put — they are platform-invariant.
 7. **Calibrate switches and icons per platform** — macOS 54×24, Windows
    40×20 with 12px knob, KDE 36×18; icon 16 on macOS/Windows.