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。

pkg/pagesarchive/extract.go

@@ -11,6 +11,9 @@ import (
 	"path/filepath"
 )
 
+// formatDetectHeadBytes is the sniff window used for archive format detection.
+const formatDetectHeadBytes = 512
+
 // ExtractOptions controls package extraction.
 type ExtractOptions struct {
 	// Limits bounds files and sizes during extraction when EnforceLimits is true.
@@ -55,7 +58,7 @@ func ExtractFile(filePath string, format Format, destDir string, opts ExtractOpt
 		return err
 	}
 	if format == "" {
-		head := make([]byte, 512)
+		head := make([]byte, formatDetectHeadBytes)
 		n, readErr := file.ReadAt(head, 0)
 		if readErr != nil && readErr != io.EOF {
 			return readErr

pkg/pagesarchive/inspect.go

@@ -42,7 +42,7 @@ func InspectFile(filePath string, format Format, opts InspectOptions) (*Manifest
 		return nil, err
 	}
 	if format == "" {
-		head := make([]byte, 512)
+		head := make([]byte, formatDetectHeadBytes)
 		n, readErr := file.ReadAt(head, 0)
 		if readErr != nil && readErr != io.EOF {
 			return nil, readErr