feat: add terminal broadcast, context menu, and shell close

Complete multi-pane broadcast, standard terminal right-click actions, batch host selection with progress, and native ssh_close_shell so closing a pane tears down the remote shell.

Co-authored-by: Cursor <cursoragent@cursor.com>

test/setup.ts

@@ -26,6 +26,7 @@ export const mockDesktopApi: DesktopApiContract = {
   sshCreateShell: vi.fn().mockResolvedValue({ success: true, shellId: 'test-shell-1' }),
   sshShellWrite: vi.fn().mockResolvedValue({ success: true }),
   sshShellResize: vi.fn().mockResolvedValue({ success: true }),
+  sshCloseShell: vi.fn().mockResolvedValue({ success: true }),
   sshForwardLocal: vi.fn().mockResolvedValue({ success: true }),
   sshForwardRemote: vi.fn().mockResolvedValue({ success: true }),
   sshForwardDynamic: vi.fn().mockResolvedValue({ success: true }),