debug(telegram): log full payload on 4xx to diagnose BUTTON_DATA_INVALID

前次 response_body 已確認錯誤碼，這次記錄完整 payload（payload_preview 前
1000 bytes）以找出觸發 BUTTON_DATA_INVALID 的確切欄位。

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/api/src/services/telegram_gateway.py

@@ -1378,6 +1378,14 @@ class TelegramGateway:
         ) as span:
             try:
                 response = await self._http_client.post(url, json=payload)
+                if response.status_code >= 400:
+                    import json as _json
+                    _payload_str = _json.dumps(payload, ensure_ascii=False)
+                    logger.error("telegram_api_rejected", method=method,
+                                 status=response.status_code,
+                                 response_body=response.text[:300],
+                                 payload_len=len(_payload_str),
+                                 payload_preview=_payload_str[:1000])
                 response.raise_for_status()
                 result = response.json()