UI: rework settings panel — card, aligned rows, themed segmented controls

The settings screen was ragged: bare gray TextButtons (off-theme), each row
center-aligned on its own so labels/controls never lined up, and a latent bug —
clicking a segment or toggle only changed the value, the highlight didn''t refresh
until Apply rebuilt the panel.

- Wrap in a Card with title + accent rule, matching the other menus.
- Every setting is a "label (fixed width) + control" row, left-aligned, so the
  controls form a clean column.
- Segments and toggles use the themed ChoiceButton with an active state
  (Ui.SetChoiceActive: accent fill/border) instead of text-color-only.
- Toggles read On/Off (new settings.on/off loc) instead of ●/○ glyphs.
- Any click now runs all refreshers immediately, so highlights track the value
  live, not just after Apply.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Mods/Core/Languages/en/ui.json

@@ -120,6 +120,8 @@
   "settings.volume": "Volume",
   "settings.uiscale": "UI scale",
   "settings.devmode": "Developer mode",
+  "settings.on": "On",
+  "settings.off": "Off",
   "dev.title": "Dev spawner",
   "dev.hint": "Pick an entry · F9 to hide",
   "dev.armed": "In hand: {0} · LMB to spawn, RMB to clear",