refac: register only open while no verified acc exists, enforced by a use case rather than handler & sends verification email whose link uses the conf pub URL whose code expires after 2h

test/user_test.go

@@ -154,7 +154,7 @@ var _ user.Repository = &mockUserRepo{}
 
 func TestCreateUser(t *testing.T) {
 	repo := newMockUserRepo()
-	uc := useCases.NewCreateUserUseCase(repo, &stubHasher{})
+	uc := useCases.NewCreateUserUseCase(repo, &stubHasher{}, newMockMailRepo(), "https://cms.example.com")
 
 	cmd := useCases.CreateUserCommand{
 		Username: "testuser",