feat(api): support traffic bytes tracking in edge access logs and refactor analytics models

- Add `bytes_sent` to `NodeAccessLog` on both Agent and Master Server.
- Create ClickHouse migration `202607120001_add_bytes_sent_to_node_access_logs.sql`.
- Refactor duplicate stats structs by centralizing them into `analyticsmodel` package with type aliases.
- Simplify access log store delegations and remove redundant mapping loops.
- Regenerate Swagger documentation.
- Update changelog index.md.

internal/model/openflare_observability.go

@@ -69,6 +69,7 @@ type OpenFlareAccessLog struct {
 	Host       string    `json:"host" gorm:"index;size:255"`
 	Path       string    `json:"path" gorm:"size:2048"`
 	StatusCode int       `json:"status_code" gorm:"index"`
+	BytesSent  int64     `json:"bytes_sent" gorm:"column:bytes_sent;not null;default:0"`
 	CreatedAt  time.Time `json:"created_at" gorm:"autoCreateTime"`
 }
 
@@ -221,6 +222,7 @@ type OpenFlareAccessLogBucketRow struct {
 	SuccessCount     int64 `json:"success_count"`
 	ClientErrorCount int64 `json:"client_error_count"`
 	ServerErrorCount int64 `json:"server_error_count"`
+	BytesSent        int64 `json:"bytes_sent"`
 }
 
 // OpenFlareAccessLogBucketIPQuery filters folded IP summary queries (v1 stub).