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/auth/handler.go

@@ -2,10 +2,10 @@ package auth
 
 import (
 	"errors"
-	"net"
 	"net/http"
 	"strings"
 
+	"hfb_sys/backend/internal/sitecode"
 	"hfb_sys/backend/pkg/response"
 
 	"github.com/gin-gonic/gin"
@@ -86,20 +86,18 @@ func (h *Handler) SendSMS(c *gin.Context) {
 		return
 	}
 
-	siteCode := strings.TrimSpace(firstNonEmpty(
-		c.GetHeader("X-Distribution-Site-Code"),
-		c.Query("distribution_site_code"),
-		c.Query("site_code"),
-		req.SiteCode,
-	))
+	siteCode := sitecode.FromRequest(c)
+	if siteCode == "" {
+		siteCode = strings.TrimSpace(req.SiteCode)
+	}
 	domain := strings.TrimSpace(firstNonEmpty(
 		c.GetHeader("X-Distribution-Domain"),
 		c.Query("distribution_domain"),
 		c.Query("domain"),
 	))
 	if siteCode == "" && domain == "" {
-		host := extractHost(c.Request.Host)
-		if host != "" && host != "localhost" && host != "127.0.0.1" && host != "::1" {
+		host := sitecode.ExtractHost(c.Request.Host)
+		if host != "" && !sitecode.IsLocalHost(host) {
 			domain = host
 		}
 	}
@@ -120,17 +118,6 @@ func firstNonEmpty(items ...string) string {
 	return ""
 }
 
-func extractHost(rawHost string) string {
-	rawHost = strings.TrimSpace(rawHost)
-	if rawHost == "" {
-		return ""
-	}
-	if host, _, err := net.SplitHostPort(rawHost); err == nil {
-		return strings.Trim(host, "[]")
-	}
-	return strings.Trim(rawHost, "[]")
-}
-
 // Login 短信验证码登录
 // @Summary      短信验证码登录
 // @Description  使用手机号和验证码登录