feat(desktop): enable multi-window support and new window action (#377)

* feat(macos): add New Window menu item

Add a New Window option to the macOS menu bar
Trigger opening a separate window when the New Window action is selected

* feat: enable multiple desktop windows and new window shortcut

Enable multiple desktop windows by extending manifest to main-*
Expose desktop_new_window to create additional windows from UI
Show New Window shortcut in Help dialog (Desktop only) with Shift + Alt + <mod> + N

* feat(desktop): enable opening host URL in new window from host switcher

Add a new action to launch a URL in a separate window from the host switcher
Wire the UI to open the selected host in a new window using a dedicated control
Expose a cross-platform API to create a new window pointing at a URL

* fix(desktop): validate URL scheme before opening new window

* fix(desktop): skip unreachable hosts when opening new windows

packages/ui/src/lib/desktopHosts.ts

@@ -108,3 +108,9 @@ export const desktopHostProbe = async (url: string): Promise<HostProbeResult> =>
   const latencyMs = readNumber(raw, 'latencyMs') ?? readNumber(raw, 'latency_ms') ?? 0;
   return { status, latencyMs };
 };
+
+export const desktopOpenNewWindowAtUrl = async (url: string): Promise<void> => {
+  const invoke = getInvoke();
+  if (!invoke) return;
+  await invoke('desktop_new_window_at_url', { url });
+};