feat(electron-backend): enable macOS title bar overlay for main window

Add macOS-specific title bar settings to the Electron main window
creation so the app uses a hidden title bar with an overlay on Darwin.
This ensures a more native, modern appearance on macOS while keeping
existing minimum size and saved bounds behavior unchanged.

apps/electron-backend/src/app/app.ts

@@ -79,6 +79,12 @@ export default class App {
             ...savedWindowBounds,
             minHeight: 600,
             minWidth: 900,
+            ...(process.platform === 'darwin'
+                ? {
+                      titleBarStyle: 'hidden',
+                      titleBarOverlay: true,
+                  }
+                : {}),
         });
         App.mainWindow.setMenu(null);
         if (!savedWindowBounds) {