refactor(settings): collapse get_all to aksrt_settings and drop migration UI

Make aksrt_settings the sole theme settings store for get_all(), remove
aksrt_seo_settings/aksrt_basic_settings merge paths, point global.logo
schema at aksrt_settings, and delete the retired settings migration page,
route, REST endpoint, and related SPA surface.

inc/classes/settings/class-aksrt-settings-credits-payment-groups.php

@@ -86,7 +86,7 @@ trait AKSRT_Settings_Credits_Payment_Groups {
     /**
      * 邀请注册功能总开关（独立于积分系统）。
      * 控制邀请链接、注册页邀请码字段、用户中心邀请卡片的显示。
-     * 存储在 aksrt_basic_settings['invite_registration_enabled']。
+     * 存储在 aksrt_settings（invit_code_s / invite_registration_enabled）。
      */
     public static function invite_registration_enabled(): bool {
         return AKSRT_Settings_Credits_Runtime::invite_registration_enabled();