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/import-export-traits/trait-aksrt-admin-import-export-controller-part-1.php

@@ -3,17 +3,6 @@ defined('ABSPATH') || exit;
 
 trait AKSRT_Admin_Import_Export_Controller_Part_1 {
 
-    public function rest_migration_status(WP_REST_Request $request): WP_REST_Response {
-        // Settings migration UI/runtime has been removed. Keep the route for old SPA chunks
-        // until the next full admin rebuild, but return an empty retired payload.
-        return $this->success([
-            'schema_version' => get_option('aksrt_db_schema_version', '0.0.0'),
-            'migration_version' => 'retired',
-            'migration_log'  => [],
-            'retired' => true,
-        ]);
-    }
-
     /**
      * Get the schema definition for a domain (for frontend introspection).
      */