Keep workspace focus mode scoped and easy to exit (#2151)

* fix(workspace): keep focus mode scoped and easy to exit

Route focus mode through the active workspace so persisted state cannot hide chrome on settings or other screens. Add a visible exit control and keep desktop window chrome aligned and visually quiet.

* fix(app): clarify muted chrome semantics

packages/app/src/desktop/host.ts

@@ -95,6 +95,7 @@ export interface DesktopWindowControlsOverlayUpdate {
   height?: number;
   backgroundColor?: string;
   foregroundColor?: string;
+  trafficLightOffsetY?: number;
 }
 
 export interface DesktopWindowBridge {