perf: optimize Cloudflare Turnstile CAPTCHA loading on login

[vlazic]

• Add <link rel="preconnect"> for challenges.cloudflare.com in base.html.twig to save ~200-500ms on DNS/TCP/TLS
• Switch Turnstile to interaction-only mode — widget is invisible unless Cloudflare needs human interaction, eliminating the visible "waiting for CAPTCHA" delay
• Handle early form submissions: if user submits before the background challenge completes, the button shows "Molimo sačekajte..." and auto-submits when the token arrives

Test plan

• Open /logovanje (not logged in), confirm no visible CAPTCHA widget appears
• Type email and submit — form should submit immediately (challenge finishes while typing)
• Test early submit (load page, immediately click submit) — button shows "Molimo sačekajte..." briefly, then auto-submits
• Check DevTools Network tab — preconnect to challenges.cloudflare.com is present
• Also test on /registracija-donatora and /postani-delegat
• Verify logged-in users see no Turnstile markup")

[Copilot]

Pull request overview

Optimizes Cloudflare Turnstile integration in Twig templates by reducing perceived latency and minimizing widget UI on user-facing forms.

Changes:

• Updates the Turnstile widget to interaction-only mode and adds client-side submit deferral until a token is available.
• Adds a preconnect hint for challenges.cloudflare.com to warm up DNS/TCP/TLS earlier.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
templates/captcha.html.twig	Switches Turnstile configuration and adds JS to delay form submission until CAPTCHA completes.
templates/base.html.twig	Adds a global preconnect hint for Cloudflare Turnstile’s domain.

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