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_user.go

@@ -1,6 +1,7 @@
 package listing
 
 import (
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 	"strings"
 
@@ -18,7 +19,7 @@ func (h *Handler) Create(c *gin.Context) {
 		response.BadRequest(c, listingBindErrorMessage(err))
 		return
 	}
-	siteCode := strings.TrimSpace(c.GetHeader("X-Distribution-Site-Code"))
+	siteCode := sitecode.FromRequest(c)
 	item, err := h.service.Create(c.Request.Context(), ownerID, req, siteCode)
 	if err != nil {
 		writeListingError(c, err)
@@ -42,7 +43,7 @@ func (h *Handler) Update(c *gin.Context) {
 		response.BadRequest(c, listingBindErrorMessage(err))
 		return
 	}
-	item, err := h.service.Update(c.Request.Context(), ownerID, id, req, strings.TrimSpace(c.GetHeader("X-Distribution-Site-Code")))
+	item, err := h.service.Update(c.Request.Context(), ownerID, id, req, sitecode.FromRequest(c))
 	if err != nil {
 		writeListingError(c, err)
 		return
@@ -103,7 +104,7 @@ func (h *Handler) ListMine(c *gin.Context) {
 		response.Unauthorized(c, "缺少用户上下文")
 		return
 	}
-	siteCode := strings.TrimSpace(c.GetHeader("X-Distribution-Site-Code"))
+	siteCode := sitecode.FromRequest(c)
 	items, err := h.service.ListMine(c.Request.Context(), ownerID, siteCode)
 	if err != nil {
 		writeListingError(c, err)