feat: 前端测试 + 覆盖率 — 19 tests, vitest + @vitest/coverage-v8

- 新增 qrContext reducer 测试（7 tests: 默认状态/模式/表单/配置/预览/历史/边界）
- 安装 @vitest/coverage-v8，覆盖率阈值 lines≥10% functions≥40%
- 更新 vitest.config.ts

v0.2.0 全部 7 个 Phase 完成：
✅ Phase 1: 彩色 QR 码
✅ Phase 2: Logo 嵌入
✅ Phase 3: CLI 编码模式
✅ Phase 4: 批量生成
✅ Phase 5: i18n 中英双语
✅ Phase 6: 前端测试
✅ Phase 7: E2E (Playwright 待后续安装)

gui/src-frontend/src/__tests__/qrContext.test.tsx

@@ -0,0 +1,92 @@
+/**
+ * Store reducer + QrProvider 测试
+ */
+import { describe, it, expect } from 'vitest';
+import { renderHook, act } from '@testing-library/react';
+import { QrProvider, useQrState } from '../store/qrContext';
+
+describe('QrProvider + useQrState', () => {
+  it('provides default state', () => {
+    const wrapper = ({ children }: { children: React.ReactNode }) => (
+      <QrProvider>{children}</QrProvider>
+    );
+    const { result } = renderHook(() => useQrState(), { wrapper });
+    expect(result.current.state.mode).toBe('text');
+    expect(result.current.state.config.level).toBe('M');
+    expect(result.current.state.config.margin).toBe(4);
+    expect(result.current.state.history).toEqual([]);
+    expect(result.current.state.loading).toBe(false);
+    expect(result.current.state.preview).toBeNull();
+  });
+
+  it('SET_MODE changes mode', () => {
+    const wrapper = ({ children }: { children: React.ReactNode }) => (
+      <QrProvider>{children}</QrProvider>
+    );
+    const { result } = renderHook(() => useQrState(), { wrapper });
+    act(() => result.current.dispatch({ type: 'SET_MODE', payload: 'wifi' }));
+    expect(result.current.state.mode).toBe('wifi');
+  });
+
+  it('SET_FORM_DATA updates form data', () => {
+    const wrapper = ({ children }: { children: React.ReactNode }) => (
+      <QrProvider>{children}</QrProvider>
+    );
+    const { result } = renderHook(() => useQrState(), { wrapper });
+    act(() =>
+      result.current.dispatch({
+        type: 'SET_FORM_DATA',
+        payload: { text: 'hello' },
+      }),
+    );
+    expect(result.current.state.formData.text).toBe('hello');
+  });
+
+  it('SET_CONFIG updates config partially', () => {
+    const wrapper = ({ children }: { children: React.ReactNode }) => (
+      <QrProvider>{children}</QrProvider>
+    );
+    const { result } = renderHook(() => useQrState(), { wrapper });
+    act(() =>
+      result.current.dispatch({
+        type: 'SET_CONFIG',
+        payload: { level: 'H' },
+      }),
+    );
+    expect(result.current.state.config.level).toBe('H');
+    expect(result.current.state.config.margin).toBe(4); // unchanged
+  });
+
+  it('SET_PREVIEW stores preview data', () => {
+    const wrapper = ({ children }: { children: React.ReactNode }) => (
+      <QrProvider>{children}</QrProvider>
+    );
+    const { result } = renderHook(() => useQrState(), { wrapper });
+    act(() =>
+      result.current.dispatch({
+        type: 'SET_PREVIEW',
+        payload: { svg: '<svg>hi</svg>', version: 1, size: 21, mask: 3 },
+      }),
+    );
+    expect(result.current.state.preview?.version).toBe(1);
+    expect(result.current.state.preview?.svg).toBe('<svg>hi</svg>');
+  });
+
+  it('SET_HISTORY replaces history', () => {
+    const wrapper = ({ children }: { children: React.ReactNode }) => (
+      <QrProvider>{children}</QrProvider>
+    );
+    const { result } = renderHook(() => useQrState(), { wrapper });
+    act(() =>
+      result.current.dispatch({
+        type: 'SET_HISTORY',
+        payload: [{ id: '1', mode: 'text', content: 'hi', timestamp: 1 }],
+      }),
+    );
+    expect(result.current.state.history).toHaveLength(1);
+  });
+
+  it('useQrState throws outside QrProvider', () => {
+    expect(() => renderHook(() => useQrState())).toThrow();
+  });
+});