fix(app): centralize window controls padding into useWindowControlsPadding hook

Replaces useTrafficLightPadding with a role-based useWindowControlsPadding
hook that absorbs all layout-conditional logic (sidebar state, focus mode,
explorer state). Consumers no longer make platform or layout decisions —
they just apply the resolved padding values.

Fixes Windows title bar overlay buttons overlapping source control icons
when the left sidebar is open, and right padding not shifting to the
explorer sidebar header when it's open.

Also fixes borderless header using borderBottomWidth:0 (layout shift)
instead of transparent, and double-click-to-maximize bounce on the
open project screen caused by nested drag handlers.

packages/app/src/constants/layout.ts

@@ -60,14 +60,3 @@ export function getIsDesktop(): boolean {
   }
   return result;
 }
-
-// Get traffic light padding values (only non-zero on desktop macOS)
-export function getTrafficLightPadding(): { left: number; top: number } {
-  if (!getIsDesktopMac()) {
-    return { left: 0, top: 0 };
-  }
-  return {
-    left: DESKTOP_TRAFFIC_LIGHT_WIDTH,
-    top: DESKTOP_TRAFFIC_LIGHT_HEIGHT,
-  };
-}