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>

shared/types/ipc.types.ts

@@ -218,6 +218,7 @@ export const IPC_CHANNELS = {
   SSH_CREATE_SHELL: 'ssh:createShell',
   SSH_SHELL_WRITE: 'ssh:shellWrite',
   SSH_SHELL_RESIZE: 'ssh:shellResize',
+  SSH_SHELL_CLOSE: 'ssh:shellClose',
   SSH_FORWARD_LOCAL: 'ssh:forwardLocal',
   SSH_FORWARD_REMOTE: 'ssh:forwardRemote',
   SSH_FORWARD_DYNAMIC: 'ssh:forwardDynamic',