[Xenro] Captcha 1.1.0

Add a self-hosted verification step to forum registration. Xenro Captcha uses ALTCHA proof-of-work challenges together with configurable request limits and an administrator activity log.

Verification runs through your own installation and does not require a third-party CAPTCHA API key or image-selection puzzles.

• Integration with XenForo's CAPTCHA provider selection.
• Bundled ALTCHA proof-of-work verification.
• Configurable challenge difficulty and lifetime.
• Registration request limits by IP address and session.
• Expired challenge and form-token renewal support.
• Administrator verification logs with configurable retention.
• Self-hosted verification assets and server-side validation.
• Compatibility with native registration forms and Xenro Auth Pages.