feat(desktop): gate traffic-lights behind window-controls style setting

Add a Window controls Style setting ('classic' | 'traffic-lights',
default 'classic') next to the existing Position setting. All four
position×style combinations render correctly with side-driven order
(close,min,max left; min,max,close right).

- Restore deleted left-classic branch (h-8 w-8 rounded-md buttons)
- Add right-traffic-lights branch (cluster with ml-1 container)
- Branch on style instead of side in WindowsWindowControls
- Store field + setter with 'classic' default (no migration needed;
  Zustand persist shallow-merges over initial state)
- Settings UI: SettingsTwoColumn with Position chips + Style dropdown
- Sanitize on client (persistence.ts) and server (settings-helpers.js)
- 10 locale dictionaries updated (add-only, no existing keys changed)
- Traffic-light button spacing 8px→10px edge-to-edge
- Delete dead DESKTOP_WINDOW_CONTROLS_WIDTH_PX constant

packages/ui/src/stores/useUIStore.ts

@@ -2254,7 +2254,7 @@ export const useUIStore = create<UIStore>()(
       {
         name: 'ui-store',
         storage: createDeferredSafeJSONStorage(),
-        version: 13,
+        version: 12,
         migrate: (persistedState, version) => {
           if (!persistedState || typeof persistedState !== 'object') {
             return persistedState;
@@ -2268,15 +2268,6 @@ export const useUIStore = create<UIStore>()(
             }
           }
 
-          // v12 -> v13: introduce window-controls style. Existing users keep
-          // their persisted position; style defaults to "classic" so no one
-          // suddenly sees traffic lights on upgrade.
-          if (version < 13) {
-            if (state.desktopWindowControlsStyle !== 'classic' && state.desktopWindowControlsStyle !== 'traffic-lights') {
-              state.desktopWindowControlsStyle = 'classic';
-            }
-          }
-
           // v10 -> v11: move the previous terminal font default forward.
           if (version < 11 && state.terminalFontSize === 13) {
             state.terminalFontSize = 14;