fix: register /cancel as a proper command

Previously /cancel was intercepted inside the 'unknown' branch, and the
comparison used the command WITHOUT the leading slash while parseCommand
returns it WITH one ('/cancel') — the check never matched, so /cancel
always fell through to the unknown-command reply, even with a pending
ask/approval.

Now a first-class command (menu included): closes the TG-side
answer/approval channel when one is pending, otherwise reports that
nothing is awaiting a reply.

lib/commands.js

@@ -95,6 +95,8 @@ export function parseCommand(text) {
         case '/new':
         case '/create':
             return { type: 'new', text };
+        case '/cancel':
+            return { type: 'cancel', text };
         default:
             return { type: 'unknown', command, text };
     }