iter(g235): 新增 copyButton 复制按钮，剪贴板写入带已复制反馈与降级（72 组件）

apps/demo/main.ts

@@ -27,6 +27,7 @@ import {
   colorPicker,
   timePicker,
   commandPalette,
+  copyButton,
   dataTable,
   datePicker,
   transfer,
@@ -1093,6 +1094,18 @@ const content = h(
     ),
     h('div', { class: 'row' }, pinInput({ value: signal(''), length: 6, disabled: true })),
   ),
+  section(
+    'sec-copybutton',
+    '复制按钮',
+    'copyButton：点击写入剪贴板，成功后短暂换成「已复制」再还原；text 可传函数取实时值，剪贴板 API 不可用时自动降级 execCommand。',
+    h(
+      'div',
+      { class: 'row' },
+      copyButton({ text: 'npm install @ui-arch/ui', onCopied: (t) => toast.success(`已复制：${t}`) }),
+      copyButton({ text: () => pinCode() || '尚未输入验证码', label: '复制上方验证码' }),
+      copyButton({ text: '禁用态示例', disabled: true }),
+    ),
+  ),
   section(
     'sec-affix',
     '固钉',