refactor: 重构项目架构，拆分代码到模块化目录

将单文件tts_server.go重构为模块化项目结构，拆分出common、dto、middleware、router、controller、service、adapter、setting等目录，优化代码组织提升可维护性

middleware/ratelimit.go

@@ -0,0 +1,101 @@
+package middleware
+
+import (
+	"net"
+	"net/http"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/volcano-tts/tts-api/common"
+)
+
+type RateLimiter struct {
+	requests    map[string][]time.Time
+	mutex       sync.Mutex
+	limit       int
+	window      time.Duration
+	lastCleanup time.Time
+}
+
+var (
+	GlobalRateLimiter *RateLimiter
+	ConcurrencySem    chan struct{}
+)
+
+func InitRateLimiter() {
+	GlobalRateLimiter = &RateLimiter{
+		requests: make(map[string][]time.Time),
+		limit:    common.RateLimitRequests,
+		window:   common.RateLimitWindow,
+	}
+	ConcurrencySem = make(chan struct{}, common.MaxConcurrentRequests)
+}
+
+func (rl *RateLimiter) Allow(key string) bool {
+	rl.mutex.Lock()
+	defer rl.mutex.Unlock()
+
+	now := time.Now()
+	cutoff := now.Add(-rl.window)
+
+	if now.Sub(rl.lastCleanup) > common.CleanupInterval {
+		rl.cleanup()
+		rl.lastCleanup = now
+	}
+
+	timestamps := rl.requests[key]
+	valid := make([]time.Time, 0, len(timestamps))
+	for _, ts := range timestamps {
+		if ts.After(cutoff) {
+			valid = append(valid, ts)
+		}
+	}
+
+	if len(valid) >= rl.limit {
+		rl.requests[key] = valid
+		return false
+	}
+
+	valid = append(valid, now)
+	rl.requests[key] = valid
+	return true
+}
+
+func (rl *RateLimiter) cleanup() {
+	cutoff := time.Now().Add(-rl.window)
+	for k, v := range rl.requests {
+		valid := make([]time.Time, 0, len(v))
+		for _, ts := range v {
+			if ts.After(cutoff) {
+				valid = append(valid, ts)
+			}
+		}
+		if len(valid) == 0 {
+			delete(rl.requests, k)
+		} else {
+			rl.requests[k] = valid
+		}
+	}
+}
+
+func GetClientIP(r *http.Request) string {
+	xForwardedFor := r.Header.Get("X-Forwarded-For")
+	if xForwardedFor != "" {
+		ips := strings.Split(xForwardedFor, ",")
+		if len(ips) > 0 {
+			return strings.TrimSpace(ips[0])
+		}
+	}
+
+	xRealIP := r.Header.Get("X-Real-IP")
+	if xRealIP != "" {
+		return xRealIP
+	}
+
+	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		return r.RemoteAddr
+	}
+	return host
+}