feat(app): ✨ implement echo api

greataped/app/commands/spi/echo.go

@@ -1,10 +1,7 @@
 package spi
 
-import (
-	. "rail.town/infrastructure/components/constants"
-	. "rail.town/infrastructure/components/contracts"
-)
+import . "rail.town/infrastructure/components/contracts"
 
 func Echo(x IDispatcher, document IDocument) (IEchoResult, error) {
-	return nil, ERROR_NOT_IMPLEMENTED
+	return x.NewEchoResult(document), nil
 }