perf(stability): add request metrics and resilient API retries

routes/health.py

@@ -9,6 +9,7 @@ from flask import Blueprint, jsonify
 
 import database
 import db_pool
+from services.request_metrics import get_request_metrics_snapshot
 from services.time_utils import get_beijing_now
 
 health_bp = Blueprint("health", __name__)
@@ -57,6 +58,11 @@ def _build_runtime_metrics() -> dict:
     except Exception:
         pass
 
+    try:
+        metrics["requests"] = get_request_metrics_snapshot()
+    except Exception:
+        pass
+
     return metrics