style: 修复前端 UI 细节问题

- 供应商/模型/统计表格增加列宽约束和 ellipsis 省略号
- 修复主题切换按钮在暗色侧边栏中不可见
- 表格添加 scroll 属性防止窄屏溢出
- 自定义表格空状态提示文案

frontend/src/__tests__/components/StatsTable.test.tsx

@@ -91,10 +91,10 @@ describe('StatsTable', () => {
   it('renders table headers correctly', () => {
     render(<StatsTable {...defaultProps} />);
 
-    expect(screen.getByText('供应商')).toBeInTheDocument();
-    expect(screen.getByText('模型')).toBeInTheDocument();
-    expect(screen.getByText('日期')).toBeInTheDocument();
-    expect(screen.getByText('请求数')).toBeInTheDocument();
+    expect(screen.getAllByText('供应商').length).toBeGreaterThanOrEqual(1);
+    expect(screen.getAllByText('模型').length).toBeGreaterThanOrEqual(1);
+    expect(screen.getAllByText('日期').length).toBeGreaterThanOrEqual(1);
+    expect(screen.getAllByText('请求数').length).toBeGreaterThanOrEqual(1);
   });
 
   it('falls back to providerId when provider not found in providers prop', () => {
@@ -108,12 +108,17 @@ describe('StatsTable', () => {
   it('renders with empty stats data', () => {
     render(<StatsTable {...defaultProps} stats={[]} />);
 
-    expect(screen.getByText('供应商')).toBeInTheDocument();
-    expect(screen.getByText('模型')).toBeInTheDocument();
+    expect(screen.getAllByText('供应商').length).toBeGreaterThanOrEqual(1);
+    expect(screen.getAllByText('模型').length).toBeGreaterThanOrEqual(1);
   });
 
   it('shows loading state', () => {
     render(<StatsTable {...defaultProps} loading={true} />);
     expect(document.querySelector('.ant-spin')).toBeInTheDocument();
   });
+
+  it('shows custom empty text when stats data is empty', () => {
+    render(<StatsTable {...defaultProps} stats={[]} />);
+    expect(screen.getByText('暂无统计数据')).toBeInTheDocument();
+  });
 });