feat: menu-bar-only app (no Dock icon) + macOS app icon

- NSApplicationActivationPolicyAccessory: app hidden from Dock and
  app switcher; lives only in the menu bar tray
- resources/clouck.icns: programmatic icon (green gradient rounded
  square, white dial, 10:10 hands), all sizes 16-1024 incl @2x
- CMake: MACOSX_BUNDLE_ICON_FILE wired, icns shipped in Resources/

window_helper_macos.mm

@@ -36,4 +36,9 @@ void MacOSWindowHelper::setupAlwaysOnTopForFullscreen(QWidget *widget)
     }
 }
 
+
+void clouck_setActivationPolicyAccessory()
+{
+    [NSApp setActivationPolicy:NSApplicationActivationPolicyAccessory];
+}
 #endif // Q_OS_MAC