HTML: Added Google reCAPTCHA v2 API script.
HTML: Inserted reCAPTCHA widget before submit button.
HTML: Disabled #check button initially.
HTML: Added CSS rule for disabled submit button inside <style>.
JS: Included 'g-recaptcha-response' in POST body.
JS: Added reCAPTCHA callbacks and guard.
JS: Submit handler now blocks if no reCAPTCHA token.
PHP: Added server-side reCAPTCHA verification to verify.php.