* fix: route Cmd+W through existing tab close flow
Keep the original tab-close behavior intact, and close the main or settings window only when there is no active closable tab to handle.
* fix: fall back to closing non-listener windows on Cmd+W
Treat BrowserWindow instances that do not participate in Netcatty's command-close bridge as regular closable windows. Keep the existing command-close path for the main and settings windows, and add tests that cover both the fallback close behavior and the renderer-capable send path.
atoz03