fix: 修复 Docker Compose 环境下 PostgreSQL 连接失败

backend/cmd/server/main.go

@@ -56,6 +56,10 @@ func main() {
 	var sessRepo store.SessionRepository
 
 	if cfg.Storage.Driver == "postgres" {
+		if cfg.Storage.DSN == "" {
+			logger.Log.Fatalw("storage.dsn is required when storage.driver is postgres",
+				"hint", "set CAMTALK_STORAGE_DSN environment variable")
+		}
 		pool, err := store.NewPostgresPool(ctx, cfg.Storage.DSN)
 		if err != nil {
 			logger.Log.Fatalw("failed to connect to postgres", "error", err)