feat(obs): 访问日志 SSOT 与 edge_health，去掉协议兼容层

Agent 仅上报 host_metrics/edge_health/access_logs；业务流量与 UV 由
Server 侧访问日志聚合。新增 of_node_edge_health 与 of_access_log_hourly，
删除 request_reports/openresty 吞吐路径；API 不再暴露 traffic_reports
与 openresty_rx|tx。心跳/离线默认阈值与回填迁移一并入库。

internal/model/analytics/node_access_log_stats.go

@@ -13,6 +13,7 @@ type NodeAccessLogBucketAggregate struct {
 	UniqueIPCount    int64 `gorm:"column:unique_ip_count"`
 	UniqueHostCount  int64 `gorm:"column:unique_host_count"`
 	BytesSent        int64 `gorm:"column:bytes_sent"`
+	RequestLength    int64 `gorm:"column:request_length"`
 }
 
 // NodeAccessLogWAFIPAggregate is a per-IP aggregate row for WAF automatic rules.