fix: /stop leaves stale paired task, sawOutput guard, progress text overwrite

- /stop now resets the active paired task to completed so the next
  user message routes to the owner instead of the stuck reviewer
- Owner completion with sawOutput=false (e.g. interrupted by /stop)
  no longer auto-triggers the reviewer — treated as interrupted
- Clear pendingProgressText when intermediate updates arrive on an
  existing progress message, preventing flushPendingProgress from
  overwriting latestProgressText with stale buffered content

src/message-turn-controller.ts

@@ -147,6 +147,7 @@ export class MessageTurnController {
             this.previousProgressText = this.latestProgressText;
             this.latestProgressText = text;
             this.latestProgressTextForFinal = text;
+            this.pendingProgressText = null; // discard stale buffer
             this.toolActivities = [];
             void this.syncTrackedProgressMessage();
           } else {