Load Turnstile site key at runtime

.env.example

@@ -23,10 +23,9 @@ JWT_SECRET=super_secret_jwt_key_123
 # --- CAPTCHA / Bot Protection (Optional) ---
 # Create keys in Cloudflare Turnstile and set both values in production.
 # When TURNSTILE_SECRET is empty, backend CAPTCHA enforcement is disabled.
+TURNSTILE_SITE_KEY=
 TURNSTILE_SECRET=
 
 # --- Frontend Configuration (Optional) ---
 # If you need to override the API URL for the frontend
 # VITE_API_URL=/api
-# Cloudflare Turnstile site key shown on the login page
-VITE_TURNSTILE_SITE_KEY=