avoid repeat captcha verify requests

[GFJHogue]

This addresses an edge case where /verify_captcha_page was sending 2 requests to /verify_captcha resulting in 400 Bad Request due to Cloudflare's single-use policy for Turnstile tokens.

1. modified the javascript to only trigger form submission once.
2. removed unnecessary turnstile .execute() call.
3. disabled caching for verify_captcha responses to prevent strange browser behaviours.

Also removed HTTPS redirection - that's now being properly handled Apache-side.