refactor(sitecode): 统一各模块分销站点编码解析为公共包

- 新增 internal/sitecode 包：FromRequest 头优先解析、FromQueryThenHeader
  探测接口专用、ExtractHost/IsLocalHost 提取 Host 域名
- 替换 auth/order/listing/chat/notification/withdrawal/wallet/distribution
  八模块 17 处各自内联的解析逻辑，统一优先级与 TrimSpace 行为
- 修复 notification 漏 TrimSpace、探测接口会话头压过显式 query、
  GetPublicSiteInfo 把 localhost Host 当站点域名查库等不一致
- 顺手清理 auth 中无引用的 extractHost 死代码
- gofmt 修复 withdrawal/presenter、chat/file/payment 测试四个历史遗留格式问题

backend/internal/modules/listing/handler_parse.go

@@ -5,6 +5,7 @@ import (
 	"strings"
 
 	"hfb_sys/backend/internal/middleware"
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -119,7 +120,7 @@ func parsePublicListQuery(c *gin.Context) PublicListQuery {
 		MinSecretKD:          parseOptionalFloat(c.Query("min_secret_kd")),
 		MaxSecretKD:          parseOptionalFloat(c.Query("max_secret_kd")),
 		ResourceRanges:       parseResourceRanges(c),
-		DistributionSiteCode: strings.TrimSpace(firstNonEmpty(c.GetHeader("X-Distribution-Site-Code"), c.Query("distribution_site_code"), c.Query("site_code"))),
+		DistributionSiteCode: sitecode.FromRequest(c),
 	}
 	if query.PageSize > 50 {
 		query.PageSize = 50