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/distribution/handler.go

@@ -7,6 +7,7 @@ import (
 	"strings"
 
 	"hfb_sys/backend/internal/middleware"
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -355,20 +356,13 @@ func (h *Handler) ListPublicSiteListings(c *gin.Context) {
 }
 
 func (h *Handler) GetPublicSiteInfo(c *gin.Context) {
-	code := strings.TrimSpace(c.Query("code"))
-	if code == "" {
-		code = strings.TrimSpace(c.Query("site_code"))
-	}
-	if code == "" {
-		code = strings.TrimSpace(c.GetHeader("X-Distribution-Site-Code"))
-	}
+	code := sitecode.FromQueryThenHeader(c)
 	domain := strings.TrimSpace(c.Query("domain"))
 	if code == "" && domain == "" {
-		host := c.Request.Host
-		if colon := strings.Index(host, ":"); colon != -1 {
-			host = host[:colon]
+		host := sitecode.ExtractHost(c.Request.Host)
+		if host != "" && !sitecode.IsLocalHost(host) {
+			domain = host
 		}
-		domain = host
 	}
 	info, err := h.service.GetPublicSiteInfo(c.Request.Context(), code, domain)
 	if err != nil {
@@ -382,14 +376,11 @@ func (h *Handler) GetPublicSiteInfo(c *gin.Context) {
 // 仅当域名属于系统中正常运行（active）的分销站点时返回 200，其余情况返回 404，
 // 防止任意外部未授权域名解析到该服务器刷爆 Let's Encrypt 证书申请配额。
 func (h *Handler) CheckDomain(c *gin.Context) {
-	domain := strings.ToLower(strings.TrimSpace(c.Query("domain")))
+	domain := sitecode.ExtractHost(c.Query("domain"))
 	if domain == "" {
 		c.String(http.StatusBadRequest, "domain required")
 		return
 	}
-	if colon := strings.Index(domain, ":"); colon != -1 {
-		domain = domain[:colon]
-	}
 
 	info, err := h.service.GetPublicSiteInfo(c.Request.Context(), "", domain)
 	if err != nil || info == nil || info.Status != "active" {