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/auth.go

@@ -0,0 +1,59 @@
+package middleware
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+	"os"
+	"strings"
+)
+
+var validAPIKeys []string
+
+func InitAPIKeys() {
+	apiKey := os.Getenv("OPENAI_TTS_API_KEY")
+	if apiKey != "" {
+		validAPIKeys = strings.Split(apiKey, ",")
+		for i, k := range validAPIKeys {
+			validAPIKeys[i] = strings.TrimSpace(k)
+		}
+		log.Printf("已配置 %d 个有效的API密钥", len(validAPIKeys))
+	} else {
+		log.Println("警告: OPENAI_TTS_API_KEY 环境变量未设置，将允许所有请求")
+	}
+}
+
+func ValidateAPIKey(r *http.Request) bool {
+	if len(validAPIKeys) == 0 {
+		return true
+	}
+
+	authHeader := r.Header.Get("Authorization")
+	if authHeader == "" {
+		return false
+	}
+
+	if !strings.HasPrefix(authHeader, "Bearer ") {
+		return false
+	}
+
+	token := strings.TrimPrefix(authHeader, "Bearer ")
+	for _, validKey := range validAPIKeys {
+		if token == validKey {
+			return true
+		}
+	}
+	return false
+}
+
+func SendJSONError(w http.ResponseWriter, statusCode int, message string, errType string, code string) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(statusCode)
+	json.NewEncoder(w).Encode(map[string]interface{}{
+		"error": map[string]interface{}{
+			"message": message,
+			"type":    errType,
+			"code":    code,
+		},
+	})
+}