feat(widgets): render icon fields with the universal icon picker

The widget FormRenderer icon case and the nav-menu item icon field now
emit the shared picker (preview + choose/clear + editable text input,
delegated events so lazy forms and repeater rows work). Icon values are
sanitized through aksrt_sanitize_icon_value on both save paths so inline
customsvg- markup survives; the widget admin screen enqueues the picker.

src/Admin/SchemaProvider.php

@@ -802,6 +802,10 @@ class SchemaProvider {
                     }
                 }
                 return $out;
+            case 'icon':
+                return function_exists('aksrt_sanitize_icon_value')
+                    ? aksrt_sanitize_icon_value((string) $value)
+                    : sanitize_text_field((string) $value);
             default:
                 return sanitize_text_field((string) $value);
         }
@@ -993,7 +997,7 @@ class SchemaProvider {
             // 自定义面板（验证码服务商等）按对象存储
             'custom'   => 'array',
             'color'    => 'string',
-            'icon'     => 'string',
+            'icon'     => 'icon',
             'media'    => 'url',
 			'upload'   => 'url',
 			'gallery'  => 'attachment_ids',