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/admin/schema/class-aksrt-admin-schema-global.php

@@ -43,7 +43,7 @@ class AKSRT_Admin_Schema_Global {
                     'key'        => 'logo',
                     'title'      => 'LOGO图像',
                     'version'    => '1.0.0',
-                    'option_key' => 'aksrt_seo_settings',
+                    'option_key' => 'aksrt_settings',
                     'groups'     => [
                         ['key' => 'logo', 'title' => 'Logo 设置', 'fields' => [
                             ['key' => 'site_logo', 'label' => '站点 Logo', 'type' => 'media', 'default' => ''],

inc/classes/admin/schema/class-aksrt-admin-schema-tools-migration.php

@@ -1,27 +0,0 @@
-<?php
-/**
- * AKSRT_Admin_Schema_Tools_Migration section schema.
- *
- * @package AKSRT
- */
-
-defined('ABSPATH') || exit;
-
-class AKSRT_Admin_Schema_Tools_Migration {
-
-    public static function build(): array {
-        return [
-            'key'        => 'migration',
-            'title'      => '数据迁移',
-            'version'    => '1.0.0',
-            'option_key' => 'aksrt_settings',
-            'groups'     => [
-                ['key' => 'status', 'title' => '迁移状态', 'fields' => [
-                    ['key' => 'current_version', 'label' => '当前版本', 'type' => 'display'],
-                    ['key' => 'pending_migrations', 'label' => '待执行迁移', 'type' => 'display'],
-                    ['key' => 'run_migration', 'label' => '执行迁移', 'type' => 'button', 'help' => '手动触发数据库迁移'],
-                ]],
-            ],
-        ];
-    }
-}