fix(captcha): close human-verification loop end-to-end

Rewrite captcha core around aksrt_captcha_config only, require captcha
on login/comment/SMS/phone auth and related gates, wire frontend token
collection, and remove dead dual-source security settings plus slider enqueue.

inc/classes/class-aksrt-auth-service.php

@@ -368,6 +368,13 @@ final class AKSRT_Auth_Service {
 			}
 		}
 
+		if (function_exists('aksrt_require_captcha')) {
+			$captcha_result = aksrt_require_captcha('login', $post);
+			if ($captcha_result !== true) {
+				return ['success' => false, 'error' => $captcha_result];
+			}
+		}
+
 		$creds = [
 			'user_login'    => $resolved_login,
 			'user_password' => (string) ($post['pwd'] ?? ''),