fix: respawn controller multi-layer detection and cleanup

- Update idle detection from legacy '↵ send' to completion message pattern
  ("for Xm Xs" time patterns like "Worked for 2m 46s")
- Add confirming_idle state for false positive prevention
- Add completionConfirmMs (5s) and noOutputTimeoutMs (30s) config options
- Add multi-layer detection with confidence scoring (0-100%)
- Fix null pointer error in extractTokenCount with guard clause
- Fix respawn controller not stopping on session cleanup (broadcast respawn:stopped)
- Update tests to use new completion message patterns
- Add detection status UI display (confidence level, waiting state)
- Update CLAUDE.md with new detection documentation

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/web/server.ts

@@ -1271,6 +1271,8 @@ export class WebServer extends EventEmitter {
       controller.stop();
       controller.removeAllListeners();
       this.respawnControllers.delete(sessionId);
+      // Notify UI that respawn is stopped for this session
+      this.broadcast('respawn:stopped', { sessionId, reason: 'session_cleanup' });
     }
 
     // Clear respawn timer
@@ -1445,6 +1447,10 @@ export class WebServer extends EventEmitter {
       this.broadcast('respawn:stepCompleted', { sessionId, step });
     });
 
+    controller.on('detectionUpdate', (detection: unknown) => {
+      this.broadcast('respawn:detectionUpdate', { sessionId, detection });
+    });
+
     controller.on('log', (message: string) => {
       this.broadcast('respawn:log', { sessionId, message });
     });