Fix worker getting stuck during sync: add timeouts, stuck detection, and safety limits

- Add invokeWithTimeout wrapper for TDLib API calls (2min timeout per call)
- Add stuck detection to getChannelMessages: break if from_message_id doesn't advance
- Add stuck detection to getTopicMessages: same protection for topic scanning
- Add stuck detection to getForumTopicList: break if pagination offsets don't advance
- Add max page limit (5000) to all scanning loops to prevent infinite pagination
- Add mutex wait timeout (30min) to prevent indefinite blocking when holder hangs
- Add cycle timeout (4h default, configurable via WORKER_CYCLE_TIMEOUT_MINUTES)
- Fix end-of-page detection to use actual limit value instead of hardcoded 100

Co-authored-by: xCyanGrizzly <53275238+xCyanGrizzly@users.noreply.github.com>

worker/dist/scheduler.d.ts

@@ -0,0 +1,13 @@
+/**
+ * Start the scheduler. Runs an immediate first cycle, then schedules subsequent ones.
+ */
+export declare function startScheduler(): Promise<void>;
+/**
+ * Trigger an immediate ingestion cycle (e.g. from the admin UI).
+ * If a cycle is already running, this is a no-op.
+ */
+export declare function triggerImmediateCycle(): Promise<void>;
+/**
+ * Stop the scheduler gracefully.
+ */
+export declare function stopScheduler(): void;