refactor: 迁移前端 antd 组件至 v6 规范 API，消除废弃用法

- 迁移静态 message 到 App.useApp() 模式，使 message 感知 ConfigProvider 上下文
- Button type/danger 迁移为 variant/color 新 API
- Space direction 迁移为 vertical 布尔属性
- Select.Option 子组件迁移为 options 属性
- AppLayout 硬编码颜色替换为 antd design token
- 优化 useThemeConfig：default/dark 改为静态导出，减少不必要的 hook 调用
- 同步更新 openspec 主规范文档

frontend/src/pages/NotFound.tsx

@@ -10,7 +10,7 @@ export function NotFound() {
       title="404"
       subTitle="抱歉，您访问的页面不存在。"
       extra={
-        <Button type="primary" onClick={() => navigate('/providers')}>
+        <Button color="primary" variant="solid" onClick={() => navigate('/providers')}>
           返回首页
         </Button>
       }

frontend/src/pages/Providers/ModelForm.tsx

@@ -68,13 +68,9 @@ export function ModelForm({
           name="providerId"
           rules={[{ required: true, message: '请选择供应商' }]}
         >
-          <Select>
-            {providers.map((p) => (
-              <Select.Option key={p.id} value={p.id}>
-                {p.name}
-              </Select.Option>
-            ))}
-          </Select>
+          <Select
+            options={providers.map((p) => ({ label: p.name, value: p.id }))}
+          />
         </Form.Item>
 
         <Form.Item

frontend/src/pages/Providers/ModelTable.tsx

@@ -35,7 +35,7 @@ export function ModelTable({ providerId, onAdd, onEdit }: ModelTableProps) {
       render: (_, record) => (
         <Space>
           {onEdit && (
-            <Button type="link" size="small" onClick={() => onEdit(record)}>
+            <Button variant="link" size="small" onClick={() => onEdit(record)}>
               编辑
             </Button>
           )}
@@ -45,7 +45,7 @@ export function ModelTable({ providerId, onAdd, onEdit }: ModelTableProps) {
             okText="确定"
             cancelText="取消"
           >
-            <Button type="link" danger size="small">
+            <Button variant="link" color="danger" size="small">
               删除
             </Button>
           </Popconfirm>
@@ -59,7 +59,7 @@ export function ModelTable({ providerId, onAdd, onEdit }: ModelTableProps) {
       <div style={{ display: 'flex', justifyContent: 'space-between', marginBottom: 8 }}>
         <span style={{ fontWeight: 500 }}>关联模型 ({models.length})</span>
         {onAdd && (
-          <Button type="link" size="small" onClick={onAdd}>
+          <Button variant="link" size="small" onClick={onAdd}>
             添加模型
           </Button>
         )}

frontend/src/pages/Providers/ProviderTable.tsx

@@ -68,7 +68,7 @@ export function ProviderTable({
       width: 160,
       render: (_, record) => (
         <Space>
-          <Button type="link" size="small" onClick={() => onEdit(record)}>
+          <Button variant="link" size="small" onClick={() => onEdit(record)}>
             编辑
           </Button>
           <Popconfirm
@@ -77,7 +77,7 @@ export function ProviderTable({
             okText="确定"
             cancelText="取消"
           >
-            <Button type="link" danger size="small">
+            <Button variant="link" color="danger" size="small">
               删除
             </Button>
           </Popconfirm>
@@ -90,7 +90,7 @@ export function ProviderTable({
     <Card
       title="供应商列表"
       extra={
-        <Button type="primary" onClick={onAdd}>
+        <Button color="primary" variant="solid" onClick={onAdd}>
           添加供应商
         </Button>
       }

frontend/src/pages/Settings/index.tsx

@@ -8,9 +8,9 @@ export function SettingsPage() {
   const { themeId, followSystem, setThemeId, setFollowSystem } = useTheme();
 
   return (
-    <Space direction="vertical" size="large" style={{ width: '100%' }}>
+    <Space vertical size="large" style={{ width: '100%' }}>
       <Card title="主题">
-        <Space direction="vertical" size="middle" style={{ width: '100%' }}>
+        <Space vertical size="middle" style={{ width: '100%' }}>
           <div style={{ display: 'flex', justifyContent: 'space-between', alignItems: 'center' }}>
             <div>
               <Text strong>主题</Text>