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/

main.cpp

@@ -49,6 +49,12 @@ int main(int argc, char *argv[])
 {
     QApplication app(argc, argv);
 
+    // Menu-bar-only app: no Dock icon, no app switcher entry.
+#ifdef Q_OS_MAC
+    extern void clouck_setActivationPolicyAccessory(); // defined in window_helper_macos.mm
+    clouck_setActivationPolicyAccessory();
+#endif
+
     app.setApplicationName("Clouck");
     app.setOrganizationName("Clouck");
     app.setApplicationDisplayName("Clouck");