refactor: 迁移 UI 组件库从 Ant Design 至 TDesign

- 替换 antd 为 tdesign-react 作为主要 UI 组件库
- 引入 Recharts 替代 @ant-design/charts 实现图表功能
- 移除主题系统相关代码（ThemeContext、themes 目录）
- 更新所有组件以适配 TDesign 组件 API
- 更新测试用例以匹配新的组件实现
- 新增 TDesign 和 Recharts 集成规范文档

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

@@ -3,8 +3,15 @@ import { describe, it, expect, vi } from 'vitest';
 import { UsageChart } from '@/pages/Stats/UsageChart';
 import type { UsageStats } from '@/types';
 
-vi.mock('@ant-design/charts', () => ({
-  Line: vi.fn(() => <div data-testid="mock-line-chart" />),
+// Mock Recharts components
+vi.mock('recharts', () => ({
+  ResponsiveContainer: vi.fn(({ children }) => <div data-testid="mock-chart-container">{children}</div>),
+  LineChart: vi.fn(() => <div data-testid="mock-line-chart" />),
+  Line: vi.fn(() => null),
+  XAxis: vi.fn(() => null),
+  YAxis: vi.fn(() => null),
+  CartesianGrid: vi.fn(() => null),
+  Tooltip: vi.fn(() => null),
 }));
 
 const mockStats: UsageStats[] = [
@@ -41,8 +48,10 @@ describe('UsageChart', () => {
   it('renders with data', () => {
     const { container } = render(<UsageChart stats={mockStats} />);
 
-    expect(container.querySelector('.ant-card')).toBeInTheDocument();
-    expect(screen.getByTestId('mock-line-chart')).toBeInTheDocument();
+    // TDesign Card component
+    expect(container.querySelector('.t-card')).toBeInTheDocument();
+    // Mocked chart container
+    expect(screen.getByTestId('mock-chart-container')).toBeInTheDocument();
   });
 
   it('renders empty state when no data', () => {
@@ -54,6 +63,9 @@ describe('UsageChart', () => {
   it('aggregates data by date correctly', () => {
     const { container } = render(<UsageChart stats={mockStats} />);
 
-    expect(container.querySelector('.ant-card')).toBeInTheDocument();
+    // TDesign Card component
+    expect(container.querySelector('.t-card')).toBeInTheDocument();
+    // Mocked chart should render
+    expect(screen.getByTestId('mock-chart-container')).toBeInTheDocument();
   });
 });