WIP: feat(captcha): implement captcha validation hooks and integrate …

[rsmithlal]

This pull request introduces extensible support for CAPTCHA validation in the user registration flow, allowing host applications to add custom security checks (such as Turnstile or reCAPTCHA) without modifying the core codebase. The changes include new hook methods in the controller, updates to the registration view for easy extension, and improved error messaging with localization.

Extensibility for CAPTCHA Validation

• Added validate_captcha_if_enabled and handle_captcha_validation_failure hook methods to BetterTogether::Users::RegistrationsController, allowing host apps to implement and customize CAPTCHA logic and error handling. Default implementations are provided and can be overridden.
• Updated the registration controller to call CAPTCHA validation before creating a user, and to handle validation failures gracefully.

View and Form Extensibility

• Added a partial _extra_registration_fields.html.erb with guidance for host apps to add custom registration fields (e.g., CAPTCHA), and rendered this partial in the registration form. [1] [2]

Localization and Error Messaging

• Added captcha_validation_failed error message to English, Spanish, and French locale files for improved user feedback on CAPTCHA failures. [1] [2] [3]

Testing

• Added controller specs to verify the default behavior of the new CAPTCHA hook methods, ensuring extensibility and reliability.