Get email template by ID.
Args: template_id: Template ID to retrieve.
Returns: Email template details.
Raises: HTTPException: 404 if template not found.
Successful Response
Response schema for email template data.
Attributes: id: Template ID (UUID string). account_id: Account ID this template belongs to. template_type: Template type identifier (e.g., 'email_verification'). locale: Language/locale code (e.g., 'en', 'es'). subject: Email subject line with Jinja2 variables. html_body: HTML email body with Jinja2 variables. text_body: Plain text email body with Jinja2 variables. enabled: Whether this template is active. is_builtin: Whether this is a built-in system template. created_at: Timestamp when the template was created. updated_at: Timestamp when the template was last updated.