弃用 OpenTelemetry，并建立日志驱动的真实慢接口基线

src/Jiaowu.Api/appsettings.json

@@ -22,6 +22,8 @@
   "Observability": {
     "Enabled": true,
     "ServiceName": "jiaowu-api",
+    "LogAllApiRequests": true,
+    "SlowRequestThresholdMilliseconds": 1000,
     "SlowQueryThresholdMilliseconds": 500,
     "IncludeSqlText": false,
     "MaximumSqlTextLength": 2000