refactor: unit testable units and cleaner dep injection

go/internal/auth/service.go

@@ -10,7 +10,7 @@ import (
 	"time"
 
 	firebaseauth "firebase.google.com/go/v4/auth"
-	"github.com/flowy-live/llink/genproto/aero"
+	pbaero "github.com/flowy-live/llink/genproto/aero"
 	"github.com/flowy-live/llink/internal/utils"
 	"github.com/redis/go-redis/v9"
 	"go.jetify.com/typeid"
@@ -112,7 +112,7 @@ func (a *authServiceImpl) RequestSignInCode(ctx context.Context, email string) e
 	}
 
 	message := fmt.Sprintf("Here is your one-time code for signing into Flowy: %s\n\nPlease do not share this with anyone.\n\nBest, \nFlowy Team", code)
-	subject := fmt.Sprintf("Sign In - Your One-Time Code for Flowy.llink")
+	subject := fmt.Sprint("Sign In - Your One-Time Code for Flowy.llink")
 	_, err = a.aeroSvc.ShootEmail(ctx, &pbaero.ShootEmailRequest{
 		ToEmails: []string{formattedEmail},
 		Subject:  subject,