fix(gateway): ignore redelivered /restart after PTB offset ACK fails (#11940)

When a Telegram /restart fires and PTB's graceful-shutdown `get_updates`
ACK call times out ("When polling for updates is restarted, updates may
be received twice" in gateway.log), the new gateway receives the same
/restart again and restarts a second time — a self-perpetuating loop.

Record the triggering update_id in `.restart_last_processed.json` when
handling /restart.  On the next process, reject a /restart whose
update_id <= the recorded one as a stale redelivery.  5-minute staleness
guard so an orphaned marker can't block a legitimately new /restart.

- gateway/platforms/base.py: add `platform_update_id` to MessageEvent
- gateway/platforms/telegram.py: propagate `update.update_id` through
  _build_message_event for text/command/location/media handlers
- gateway/run.py: write dedup marker in _handle_restart_command;
  _is_stale_restart_redelivery checks it before processing /restart
- tests/gateway/test_restart_redelivery_dedup.py: 9 new tests covering
  fresh restart, redelivery, staleness window, cross-platform,
  malformed-marker resilience, and no-update_id (CLI) bypass

Only active for Telegram today (the one platform with monotonic
cross-session update ordering); other platforms return False from
_is_stale_restart_redelivery and proceed normally.

gateway/platforms/base.py

@@ -669,6 +669,15 @@ class MessageEvent:
     # Original platform data
     raw_message: Any = None
     message_id: Optional[str] = None
+
+    # Platform-specific update identifier.  For Telegram this is the
+    # ``update_id`` from the PTB Update wrapper; other platforms currently
+    # ignore it.  Used by ``/restart`` to record the triggering update so the
+    # new gateway can advance the Telegram offset past it and avoid processing
+    # the same ``/restart`` twice if PTB's graceful-shutdown ACK times out
+    # ("Error while calling `get_updates` one more time to mark all fetched
+    # updates" in gateway.log).
+    platform_update_id: Optional[int] = None
     
     # Media attachments
     # media_urls: local file paths (for vision tool access)