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

router/router.go

@@ -0,0 +1,27 @@
+package router
+
+import (
+	"net/http"
+
+	"github.com/gorilla/mux"
+	"github.com/volcano-tts/tts-api/controller"
+	"github.com/volcano-tts/tts-api/middleware"
+)
+
+func Setup() *mux.Router {
+	r := mux.NewRouter()
+
+	r.Use(middleware.CORS)
+	r.Use(middleware.Logger)
+
+	r.HandleFunc("/v1/audio/speech", controller.OpenaiTTSHandler).Methods("POST", "OPTIONS")
+	r.HandleFunc("/health", controller.HealthHandler).Methods("GET")
+	r.HandleFunc("/dashboard", func(w http.ResponseWriter, r *http.Request) {
+		http.ServeFile(w, r, "health.html")
+	}).Methods("GET")
+	r.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, "/dashboard", http.StatusFound)
+	}).Methods("GET")
+
+	return r
+}