fix(telegram): wire sendPollTelegram into channel action handler (#16977)

The Telegram channel adapter listed no 'poll' action, so agents could
not create polls via the unified action interface. The underlying
sendPollTelegram function was already implemented but unreachable.

Changes:
- telegram.ts: add 'poll' to listActions (enabled by default via gate),
  add handleAction branch that reads pollQuestion/pollOption params and
  delegates to handleTelegramAction with action 'sendPoll'.
- telegram-actions.ts: add 'sendPoll' handler that validates question,
  options (≥2), and forwards to sendPollTelegram with threading, silent,
  and anonymous options.
- actions.test.ts: add test verifying poll action routes correctly.

Fixes #16977

src/config/types.telegram.ts

@@ -18,6 +18,8 @@ export type TelegramActionConfig = {
   polls?: boolean;
   deleteMessage?: boolean;
   editMessage?: boolean;
+  /** Enable poll actions (sendPoll). */
+  poll?: boolean;
   /** Enable sticker actions (send and search). */
   sticker?: boolean;
 };