Improve email verification flow and error handling

- Send verification email before creating user to prevent orphaned accounts
- Detect SMTP authentication errors and fail fast without retries
- Add field-level validation errors for better frontend UX
- Configure docker-compose with explicit environment variables
- Document dollar sign escaping in .env.example (use $$)
- Implement welcome email on successful verification
- Clean up unnecessary comments

internal/application/queries/refresh_token_test.go

@@ -67,6 +67,10 @@ func (m *mockUserRepositoryForRefresh) Update(ctx context.Context, user *entitie
 	return nil
 }
 
+func (m *mockUserRepositoryForRefresh) Delete(ctx context.Context, id string) error {
+	return nil
+}
+
 func TestRefreshTokenHandler_Success(t *testing.T) {
 	refreshTokenRepo := &mockRefreshTokenRepository{
 		findByTokenFunc: func(ctx context.Context, token string) (*entities.RefreshToken, error) {