build: 升级go版本到1.26并添加限流中间件

1.  调整go.mod将Go版本升级至1.26
2.  新增速率限制和并发限制中间件，将其加入路由中间件链
3.  重构TTS处理逻辑，将限流逻辑迁移至中间件统一处理
4.  优化CORS中间件代码，移除冗余日志和格式调整

middleware/ratelimit_middleware.go

@@ -0,0 +1,32 @@
+package middleware
+
+import (
+	"log"
+	"net/http"
+)
+
+func RateLimit(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		clientIP := GetClientIP(r)
+		if !GlobalRateLimiter.Allow(clientIP) {
+			log.Printf("警告: 已超过IP速率限制，拒绝请求 - 客户端IP: %s", clientIP)
+			SendJSONError(w, http.StatusTooManyRequests, "Rate limit exceeded. Please try again later.", "rate_limit_error", "rate_limit_exceeded")
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}
+
+func ConcurrencyLimit(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		select {
+		case ConcurrencySem <- struct{}{}:
+			defer func() { <-ConcurrencySem }()
+			next.ServeHTTP(w, r)
+		default:
+			log.Printf("警告: 已达到最大并发请求数限制，拒绝请求 - 客户端IP: %s", GetClientIP(r))
+			SendJSONError(w, http.StatusServiceUnavailable, "Server is busy, maximum concurrent requests reached. Please try again later.", "concurrency_limit_error", "max_concurrent_requests")
+			return
+		}
+	})
+}