fix(gateway): 修复 usage_logs 记录 IP 不正确的问题

在 nginx 反向代理场景下，使用 ip.GetClientIP() 替代 c.ClientIP()
以正确获取客户端真实 IP 地址

backend/internal/handler/gateway_handler.go

@@ -15,6 +15,7 @@ import (
 	"github.com/Wei-Shaw/sub2api/internal/pkg/antigravity"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/claude"
 	pkgerrors "github.com/Wei-Shaw/sub2api/internal/pkg/errors"
+	"github.com/Wei-Shaw/sub2api/internal/pkg/ip"
 	"github.com/Wei-Shaw/sub2api/internal/pkg/openai"
 	middleware2 "github.com/Wei-Shaw/sub2api/internal/server/middleware"
 	"github.com/Wei-Shaw/sub2api/internal/service"
@@ -291,10 +292,10 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 
 			// 捕获请求信息（用于异步记录，避免在 goroutine 中访问 gin.Context）
 			userAgent := c.GetHeader("User-Agent")
-			clientIP := c.ClientIP()
+			clientIP := ip.GetClientIP(c)
 
 			// 异步记录使用量（subscription已在函数开头获取）
-			go func(result *service.ForwardResult, usedAccount *service.Account, ua, ip string) {
+			go func(result *service.ForwardResult, usedAccount *service.Account, ua, clientIP string) {
 				ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 				defer cancel()
 				if err := h.gatewayService.RecordUsage(ctx, &service.RecordUsageInput{
@@ -304,7 +305,7 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 					Account:      usedAccount,
 					Subscription: subscription,
 					UserAgent:    ua,
-					IPAddress:    ip,
+					IPAddress:    clientIP,
 				}); err != nil {
 					log.Printf("Record usage failed: %v", err)
 				}
@@ -425,10 +426,10 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 
 		// 捕获请求信息（用于异步记录，避免在 goroutine 中访问 gin.Context）
 		userAgent := c.GetHeader("User-Agent")
-		clientIP := c.ClientIP()
+		clientIP := ip.GetClientIP(c)
 
 		// 异步记录使用量（subscription已在函数开头获取）
-		go func(result *service.ForwardResult, usedAccount *service.Account, ua, ip string) {
+		go func(result *service.ForwardResult, usedAccount *service.Account, ua, clientIP string) {
 			ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 			defer cancel()
 			if err := h.gatewayService.RecordUsage(ctx, &service.RecordUsageInput{
@@ -438,7 +439,7 @@ func (h *GatewayHandler) Messages(c *gin.Context) {
 				Account:      usedAccount,
 				Subscription: subscription,
 				UserAgent:    ua,
-				IPAddress:    ip,
+				IPAddress:    clientIP,
 			}); err != nil {
 				log.Printf("Record usage failed: %v", err)
 			}