后台同步异常时前端显示错误提示，不再卡住页面

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ft-app/app/collector.py

@@ -5,7 +5,7 @@ from app.database import SessionLocal
 from app.models import DailyBar, Contract
 from app.engine.lock_strategy import compute_amp_5d
 
-_progress = {"running": False, "label": "", "done": 0, "total": 0, "result": 0, "finished": False}
+_progress = {"running": False, "label": "", "done": 0, "total": 0, "result": 0, "finished": False, "error": ""}
 _lock = threading.Lock()
 
 
@@ -18,11 +18,14 @@ def _start_bg(target, label):
     with _lock:
         if _progress["running"]:
             return False
-        _progress.update(running=True, finished=False, label=label, done=0, total=0)
+        _progress.update(running=True, finished=False, label=label, done=0, total=0, error="")
 
     def _run():
         try:
             target()
+        except Exception as e:
+            with _lock:
+                _progress["error"] = str(e)
         finally:
             with _lock:
                 _progress["running"] = False