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

dto/tts.go

@@ -0,0 +1,40 @@
+package dto
+
+import "time"
+
+type OpenAITTSRequest struct {
+	Model          string  `json:"model"`
+	Input          string  `json:"input"`
+	Voice          string  `json:"voice"`
+	ResponseFormat string  `json:"response_format,omitempty"`
+	Speed          float64 `json:"speed,omitempty"`
+}
+
+type V3TTSResponse struct {
+	ReqID    string   `json:"reqid"`
+	Code     int      `json:"code"`
+	Message  string   `json:"message"`
+	Event    string   `json:"event"`
+	Sequence int      `json:"sequence"`
+	Data     string   `json:"data"`
+	Sentence string   `json:"sentence,omitempty"`
+	IsFinal  bool     `json:"is_final"`
+	Usage    *V3Usage `json:"usage,omitempty"`
+}
+
+type V3Usage struct {
+	TextWords int `json:"text_words"`
+}
+
+type ByteDanceTTSConfig struct {
+	ApiKey     string
+	ResourceId string
+	Speaker    string
+	URL        string
+	Timeout    time.Duration
+}
+
+type SynthesisResult struct {
+	AudioData []byte
+	ReqID     string
+}