feat(KB-249): immediate stuck task check on timeout setting change

- Add checkNow() method to StuckTaskDetector for immediate stuck task detection\n- Add comprehensive tests for checkNow() method\n- Wire up settings change handler in dashboard command\n- Update AGENTS.md documentation with immediate check behavior

packages/engine/src/stuck-task-detector.ts

@@ -56,6 +56,7 @@ export class StuckTaskDetector {
   start(): void {
     if (this.interval) return;
     this.interval = setInterval(() => {
+      stuckLog.log("Running periodic stuck task check (polling)");
       this.checkStuckTasks().catch((err) => {
         stuckLog.error("Error checking stuck tasks:", err);
       });
@@ -173,6 +174,16 @@ export class StuckTaskDetector {
     this.onStuck?.(taskId);
   }
 
+  /**
+   * Check for stuck tasks immediately, outside the normal polling cycle.
+   * Safe to call at any time — will no-op if no tasks are tracked or timeout is disabled.
+   * Logs at debug level to distinguish manual checks from polling.
+   */
+  async checkNow(): Promise<void> {
+    stuckLog.log("Running immediate stuck task check (triggered manually)");
+    await this.checkStuckTasks();
+  }
+
   /**
    * Poll all tracked tasks and kill any that have exceeded the timeout.
    * Reads `taskStuckTimeoutMs` from settings on each check so changes