chore: embed health.html 到 binary,单文件分发

把 health.html 从外部依赖改为 //go:embed 内嵌,
实现真正的"单 exe 分发"。

  - 新建 router/dashboard.go,用 //go:embed 嵌入 health.html
  - router/router.go:/dashboard handler 改为 w.Write(dashboardHTML)
  - setting/config.go:删 CheckStaticFiles(无需文件检查)
  - main.go:删 setting.CheckStaticFiles() 调用
  - Dockerfile:删 COPY health.html 步骤(已嵌入)
  - .gitignore:加 release/(build 产物不入 git)
  - 物理移动 health.html 到 router/(embed 限制:同包或子包)

效果:
  - 之前: release 包 = tts-api.exe + health.html (2 个文件)
  - 之后: release 包 = tts-api.exe (1 个文件,~7 MB)
  - 用户部署无需额外文件,/dashboard 路由直接工作

router/router.go

@@ -20,7 +20,8 @@ func Setup() *mux.Router {
 	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")
+		w.Header().Set("Content-Type", "text/html; charset=utf-8")
+		w.Write(dashboardHTML)
 	}).Methods("GET")
 	r.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
 		http.Redirect(w, r, "/dashboard", http.StatusFound)