fix(zopk): Add heartbeat to knowledge extraction SSE stream

Long-running Gemini extractions (30-120s per article) caused SSE
connection timeout. Now runs extraction in a thread and sends
heartbeat updates every 10s to keep the connection alive.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

blueprints/admin/routes_zopk_knowledge.py

@@ -229,7 +229,21 @@ def admin_zopk_knowledge_extract_stream():
                 # Send processing update
                 yield f"data: {json.dumps({'current': idx, 'total': total, 'percent': round((idx-1)/total*100, 1), 'stage': 'extracting', 'status': 'processing', 'message': f'Analizuję AI: {article.title[:50]}...', 'article_id': article.id, 'article_title': article.title[:80], 'details': stats}, ensure_ascii=False)}\n\n"
 
-                result = service.extract_from_news(article.id)
+                # Run extraction in thread with heartbeats to prevent SSE timeout
+                import threading
+                extract_result = [None]
+                def _extract():
+                    extract_result[0] = service.extract_from_news(article.id)
+                t = threading.Thread(target=_extract)
+                t.start()
+                heartbeat_count = 0
+                while t.is_alive():
+                    t.join(timeout=10)
+                    if t.is_alive():
+                        heartbeat_count += 1
+                        elapsed = round(time.time() - start_time)
+                        yield f"data: {json.dumps({'current': idx, 'total': total, 'percent': round((idx-1)/total*100, 1), 'stage': 'extracting', 'status': 'processing', 'message': f'Analizuję AI: {article.title[:50]}... ({elapsed}s)', 'details': stats}, ensure_ascii=False)}\n\n"
+                result = extract_result[0]
 
                 if result.success:
                     stats['success'] += 1