fix(server): 添加YMT DSN检查并支持动态端口配置

当YMT DSN为空时跳过迁移
从环境变量读取端口号，默认使用8080

server/cmd/server/main.go

@@ -33,12 +33,17 @@ func main() {
     if err != nil {
         log.Fatal(err)
     }
-    if err := migrate.Apply(ymt); err != nil {
+    if ymtDSN != "" {
-        log.Fatal(err)
+        if err := migrate.Apply(ymt); err != nil {
+            log.Fatal(err)
+        }
+    } else {
+        log.Println("skip migrations: YMT DSN missing")
     }
     r := api.NewRouter(ymt, marketing)
-    srv := &http.Server{Addr: ":8080", Handler: r, ReadTimeout: 15 * time.Second, WriteTimeout: 60 * time.Second}
+    addr := ":" + func() string { s := os.Getenv("PORT"); if s == "" { return "8080" }; return s }()
-    log.Println("server listening on :8080")
+    srv := &http.Server{Addr: addr, Handler: r, ReadTimeout: 15 * time.Second, WriteTimeout: 60 * time.Second}
+    log.Println("server listening on ", addr)
     log.Fatal(srv.ListenAndServe())
 }