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.

assets/admin/src/pages/theme/ThemeInfoPage.vue

@@ -1,6 +1,6 @@
 <template>
   <div class="aksrt-page-container">
-    <PageHeader title="主题信息" desc="主题版本、运行环境、已启用模块、迁移状态和关键系统信息。" />
+    <PageHeader title="主题信息" desc="主题版本、运行环境、已启用模块和关键系统信息。" />
 
     <div v-if="loading" class="aksrt-theme-info__loading">
       <n-spin size="medium" />
@@ -24,9 +24,6 @@
           <n-descriptions-item label="数据库 Schema">
             <n-tag type="info" size="small">{{ info.dbSchemaVersion }}</n-tag>
           </n-descriptions-item>
-          <n-descriptions-item label="设置迁移版本">
-            <n-tag type="info" size="small">{{ info.settingsMigrationVersion || '未迁移' }}</n-tag>
-          </n-descriptions-item>
           <n-descriptions-item label="邮箱验证回填">
             <n-tag :type="info.emailBackfillDone ? 'success' : 'default'" size="small">
               {{ info.emailBackfillDone ? '已完成' : '未触发' }}
@@ -135,7 +132,6 @@ const info = ref({
   wpVersion: '',
   phpVersion: '',
   dbSchemaVersion: '',
-  settingsMigrationVersion: '',
   emailBackfillDone: false,
   siteUrl: '',
   apiUrl: '',
@@ -181,7 +177,6 @@ onMounted(async () => {
       wpVersion: data.wp_version || '',
       phpVersion: data.php_version || '',
       dbSchemaVersion: data.db_schema_version || '',
-      settingsMigrationVersion: data.settings_migration_version || '',
       emailBackfillDone: !!data.email_backfill_done,
       siteUrl: data.site_url || window.aksrtAdminData?.siteUrl || '',
       apiUrl: data.api_url || window.aksrtAdminData?.apiUrl || '',