feat(phase2): shared common-form layer + CommonWidgetFields trait for all widgets

- Extract Zibll CSF_Widget::params() common-field parity into
  inc/modules/widget-common.php (required by widgets-register.php to keep
  both files <1000 lines): subtitle, title_style(simple/big), title_highlight
  +color, title_link x3, title_link_style colors, sidebar_affix, show_type
  (all/only_pc/only_sm), show_id_type(show/hide), show_ids, animation_in,
  animation_repeat, layout_pin_pc/m, layout_bg(white/dark). Adds
  normalize_link/normalize_bg helpers, affix_attrs, common_wrapper_attr,
  render_title, animation_class. Back-compat normalizes legacy tokens
  (in_affix->sidebar_affix, pc/only_pc, include/exclude->show/hide).
- Add src/AKSRT/Widgets/Traits/CommonWidgetFields.php trait
  (render_common_form_section + update_common_fields).
- Wire all 57 widgets to use the trait; migrate the 16 hand-rolled in_affix
  implementations to shared sidebar_affix (fixes 6 latent bugs where
  in_affix was never persisted). SearchWidget intentionally skips the shared
  form section (its business show_type collides) but adopts the affix helper.
- widget_display_callback parity verified via tmp assertion script.

Refs .specs/plans/zibll-widgets-1to1.md Phase 2 (US1/US5)

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

src/AKSRT/Widgets/WidgetLangSwitch.php

@@ -7,9 +7,13 @@
 
 namespace AKSRT\Widgets;
 
+use AKSRT\Widgets\Traits\CommonWidgetFields;
+
 defined('ABSPATH') || exit;
 
 class WidgetLangSwitch extends \WP_Widget {
+	use CommonWidgetFields;
+
 
 	public function __construct() {
 		parent::__construct(
@@ -101,7 +105,8 @@ class WidgetLangSwitch extends \WP_Widget {
 		</p>
 		<p><small><?php esc_html_e('需要安装 Polylang 或 WPML 等多语言插件才能生效。', 'aksrt'); ?></small></p>
 		<?php
-	}
+			$this->render_common_form_section($instance);
+}
 
 	/**
 	 * @param array<string,mixed> $new_instance
@@ -113,11 +118,11 @@ class WidgetLangSwitch extends \WP_Widget {
 		if (!in_array($style, ['dropdown', 'flags', 'inline'], true)) {
 			$style = 'dropdown';
 		}
-		return [
+		$business = [
 			'title'        => sanitize_text_field((string) ($new_instance['title'] ?? '')),
 			'style'        => $style,
 			'show_name'    => !empty($new_instance['show_name']) ? 1 : 0,
 			'hide_current' => !empty($new_instance['hide_current']) ? 1 : 0,
-		];
+		]; return $this->update_common_fields($new_instance, $old_instance, $business);
 	}
 }