feat(widgets): rebuild admin widgets page to match reference theme

- Replace transfer modal/admin-post flow with reference-style AJAX
  export/import/template dialogs (admin-transfer.js, TransferController)
- Customizer "移出模块" action, reference lazy form loading with t-notice
- Common fields use reference labels, dependencies, compact/inline rows,
  top/bottom-only extra spacing; form header with description/reminder
- Remove placement hint, template preview and legacy transfer code
- Fix widget audit (current_datetime stub, honor catalog common flags)
  and regenerate stale golden fixtures for posts_toc, quote, posts

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tools/audit-widget-system.php

@@ -133,8 +133,15 @@ foreach ($registry as $slug => $definition) {
 	$fields = $definition->fields();
 	$walk($fields, $slug);
 	$field_ids = array_column($fields, 'id');
-	$required_common = ['show_type', 'show_id_type', 'show_ids', 'layout_pin_pc', 'layout_bg'];
-	if (($definition->common()['animation'] ?? true)) {
+	$flags = $definition->common();
+	$required_common = [];
+	if (!empty($flags['visibility'])) {
+		array_push($required_common, 'show_type', 'show_id_type', 'show_ids');
+	}
+	if (!empty($flags['layout'])) {
+		array_push($required_common, 'layout_pin_pc', 'layout_bg');
+	}
+	if (!empty($flags['animation'])) {
 		$required_common[] = 'animation_in';
 	}
 	foreach ($required_common as $required) {
@@ -164,6 +171,11 @@ foreach ($expected as $slug) {
 if (!defined('DAY_IN_SECONDS')) {
 	define('DAY_IN_SECONDS', 86400);
 }
+if (!function_exists('current_datetime')) {
+	function current_datetime(): DateTimeImmutable {
+		return new DateTimeImmutable('now', new DateTimeZone('UTC'));
+	}
+}
 $query_args = PostQuery::arguments([
 	'count' => 7,
 	'category_ids' => '2,5',