Cloudflare Turnstile en login y registro (Next.js)

- lib/turnstile.ts: verifyTurnstile(token, ip) contra siteverify (fail-closed).
- components/Turnstile.tsx: widget cliente (carga el script de Cloudflare, callback
  con el token). Site key por NEXT_PUBLIC_TURNSTILE_SITE_KEY; secreto server-only.
- LoginForm/RegisterForm: widget + token en el POST; submit deshabilitado hasta
  resolver el captcha (si hay site key).
- Routes login/register: verifican el token antes de continuar (error captchaFailed).
- Catálogos: captchaFailed.

Verificado: POST sin token -> captchaFailed en login y registro (enforcement server).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

web-next/messages/en.json

@@ -37,7 +37,8 @@
     "genericError": "Something went wrong. Please try again later.",
     "forgot": "I forgot my password/username",
     "newHere": "New to the community? You can create an account",
-    "createAccount": "here"
+    "createAccount": "here",
+    "captchaFailed": "Anti-bot verification failed. Please retry."
   },
   "Account": {
     "title": "My account",
@@ -71,7 +72,8 @@
     "invalidEmail": "The email address is not valid.",
     "emailExists": "An account with that email already exists.",
     "recruiterNotFound": "The recruiter entered does not exist.",
-    "genericError": "Something went wrong. Please try again later."
+    "genericError": "Something went wrong. Please try again later.",
+    "captchaFailed": "Anti-bot verification failed. Please retry."
   },
   "Activate": {
     "activating": "Activating your account…",