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>

src/desktop.d.ts

@@ -28,6 +28,7 @@ export interface DesktopApiContract {
   ) => Promise<{ success: boolean; shellId?: string; error?: string }>
   sshShellWrite: (shellId: string, data: string | Uint8Array) => Promise<{ success: boolean; error?: string }>
   sshShellResize: (shellId: string, cols: number, rows: number) => Promise<{ success: boolean; error?: string }>
+  sshCloseShell: (shellId: string) => Promise<{ success: boolean; error?: string }>
   // Local terminal (host shell)
   localListShells: () => Promise<{
     success: boolean