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

setting/config.go

@@ -0,0 +1,91 @@
+package setting
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"time"
+
+	"github.com/volcano-tts/tts-api/common"
+	"github.com/volcano-tts/tts-api/dto"
+)
+
+var (
+	TTSConfig    dto.ByteDanceTTSConfig
+	TTSConfigErr error
+)
+
+func InitTTSConfig() error {
+	apiKey := os.Getenv("BYTEDANCE_TTS_API_KEY")
+	resourceId := os.Getenv("BYTEDANCE_TTS_RESOURCE_ID")
+	speaker := os.Getenv("BYTEDANCE_TTS_SPEAKER")
+
+	missingVars := []string{}
+	if apiKey == "" {
+		missingVars = append(missingVars, "BYTEDANCE_TTS_API_KEY")
+	}
+	if resourceId == "" {
+		missingVars = append(missingVars, "BYTEDANCE_TTS_RESOURCE_ID")
+	}
+	if speaker == "" {
+		missingVars = append(missingVars, "BYTEDANCE_TTS_SPEAKER")
+	}
+
+	if len(missingVars) > 0 {
+		return fmt.Errorf("缺少必需的环境变量: %v", missingVars)
+	}
+
+	url := "https://openspeech.bytedance.com/api/v3/tts/unidirectional"
+
+	timeout := common.DefaultTimeout
+	if timeoutStr := os.Getenv("BYTEDANCE_TTS_TIMEOUT"); timeoutStr != "" {
+		if parsedTimeout, err := time.ParseDuration(timeoutStr); err == nil {
+			timeout = parsedTimeout
+		} else {
+			log.Printf("无效的超时设置 '%s'，使用默认值: %v", timeoutStr, timeout)
+		}
+	}
+
+	TTSConfig = dto.ByteDanceTTSConfig{
+		ApiKey:     apiKey,
+		ResourceId: resourceId,
+		Speaker:    speaker,
+		URL:        url,
+		Timeout:    timeout,
+	}
+	return nil
+}
+
+func CheckEnvironmentVariables() map[string]interface{} {
+	requiredVars := map[string]bool{
+		"BYTEDANCE_TTS_API_KEY":     os.Getenv("BYTEDANCE_TTS_API_KEY") != "",
+		"BYTEDANCE_TTS_RESOURCE_ID": os.Getenv("BYTEDANCE_TTS_RESOURCE_ID") != "",
+		"BYTEDANCE_TTS_SPEAKER":     os.Getenv("BYTEDANCE_TTS_SPEAKER") != "",
+	}
+
+	missingVars := []string{}
+	for varName, isSet := range requiredVars {
+		if !isSet {
+			missingVars = append(missingVars, varName)
+		}
+	}
+
+	optionalVars := map[string]bool{
+		"BYTEDANCE_TTS_TIMEOUT": os.Getenv("BYTEDANCE_TTS_TIMEOUT") != "",
+		"OPENAI_TTS_API_KEY":    os.Getenv("OPENAI_TTS_API_KEY") != "",
+		"PORT":                  os.Getenv("PORT") != "",
+	}
+
+	return map[string]interface{}{
+		"all_required_vars_set": len(missingVars) == 0,
+		"missing_required_vars": missingVars,
+		"required_vars_set":     requiredVars,
+		"optional_vars_set":     optionalVars,
+	}
+}
+
+func CheckStaticFiles() {
+	if _, err := os.Stat("health.html"); os.IsNotExist(err) {
+		log.Println("警告: health.html 不存在，/dashboard 路由将返回 404")
+	}
+}