refactor(permissions): remove hard-off compat stubs and harden login schema

Delete aksrt-compat.php and rewire messages/PM entry points to the user
center notification route. Normalize permissions login dependsOn objects
and allow an explicit empty captcha provider option so login/moderation
schema pages remain loadable without legacy compatibility shims.

inc/helpers/aksrt-compat.php

@@ -1,40 +0,0 @@
-<?php
-/**
- * Deprecated compatibility toggles retained only as hard-off stubs.
- *
- * The rebuild now treats Zibll-style mainline pages as the only product target.
- * Historical message center / PM entry points / compat template pickers stay on
- * disk for legacy routing safety, but no longer participate in product-facing
- * navigation or configuration decisions.
- *
- * @package AKSRT
- */
-
-defined('ABSPATH') || exit;
-
-if (!function_exists('aksrt_get_messages_url')) {
-    /**
-     * Legacy message center URL stub.
-     */
-    function aksrt_get_messages_url(): string {
-        return home_url('/messages/');
-    }
-}
-
-if (!function_exists('aksrt_pm_frontend_enabled')) {
-    /**
-     * Private-message entry is disabled in the rebuilt mainline.
-     */
-    function aksrt_pm_frontend_enabled(): bool {
-        return false;
-    }
-}
-
-if (!function_exists('aksrt_show_compat_page_templates')) {
-    /**
-     * Compat-only page templates are hidden from the rebuilt product surface.
-     */
-    function aksrt_show_compat_page_templates(): bool {
-        return false;
-    }
-}

inc/helpers/aksrt-user-center.php

@@ -453,7 +453,7 @@ if (!function_exists('aksrt_get_user_center_render_context')) {
 			'show_avatar_edit'          => !empty($user_center_settings['avatar_upload']),
 			'avatar_settings_url'       => admin_url('profile.php'),
 			'notification_unread_count' => function_exists('aksrt_get_user_unread_notification_count') ? aksrt_get_user_unread_notification_count($user_id) : 0,
-			'messages_url'              => function_exists('aksrt_get_messages_url') ? aksrt_get_messages_url() : aksrt_get_user_center_url('notif'),
+			'messages_url'              => aksrt_get_user_center_url('notif'),
 			'per_page'                  => 10,
 			'posts_page'                => max(1, isset($_GET['posts_page']) ? (int) $_GET['posts_page'] : 1),
 			'comments_page'             => max(1, isset($_GET['comments_page']) ? (int) $_GET['comments_page'] : 1),