Show the app as Starsync (window titles, launcher entry, About, README); internals unchanged

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/windows/runner/main.cpp

@@ -27,7 +27,7 @@ int APIENTRY wWinMain(_In_ HINSTANCE instance, _In_opt_ HINSTANCE prev,
   FlutterWindow window(project);
   Win32Window::Point origin(10, 10);
   Win32Window::Size size(1280, 720);
-  if (!window.Create(L"watch_together", origin, size)) {
+  if (!window.Create(L"Starsync", origin, size)) {
     return EXIT_FAILURE;
   }
   window.SetQuitOnClose(true);