🐛 fix(ui): 修复新版 UI 布局回归并恢复切换样式

- 修复 v2 下 App 外层旧版左侧控件叠加问题，由新版 Sidebar 完整接管左侧布局
- 隔离旧版 AI 悬浮入口和 SQL 日志入口，避免影响新版 UI
- 恢复主题设置中界面版本切换的双卡片样式，移除胶囊分段控件
- 补齐 v2 主题样式、全局字体变量和弹窗按需挂载逻辑
- 增加回归测试锁定新版左侧布局和界面版本切换样式

frontend/src/App.ui-version.test.ts

@@ -0,0 +1,47 @@
+import { describe, expect, it } from 'vitest';
+import { readFileSync } from 'node:fs';
+import { fileURLToPath } from 'node:url';
+
+const appSource = readFileSync(
+  fileURLToPath(new globalThis.URL('./App.tsx', import.meta.url)),
+  'utf8',
+);
+
+describe('UI version switch placement', () => {
+  it('loads the v2 theme stylesheet with the app shell', () => {
+    expect(appSource).toContain("import './App.css';");
+    expect(appSource).toContain("import './v2-theme.css';");
+  });
+
+  it('keeps the UI version switch in theme mode and outside macOS-only settings', () => {
+    const themeBranchIndex = appSource.indexOf("{themeModalSection === 'theme' ? (");
+    const uiVersionIndex = appSource.indexOf('界面版本', themeBranchIndex);
+    const lightThemeIndex = appSource.indexOf('亮色主题', themeBranchIndex);
+    const appearanceBranchIndex = appSource.indexOf(') : (', themeBranchIndex);
+    const macWindowIndex = appSource.indexOf('macOS 窗口控制');
+
+    expect(themeBranchIndex).toBeGreaterThan(-1);
+    expect(uiVersionIndex).toBeGreaterThan(themeBranchIndex);
+    expect(uiVersionIndex).toBeLessThan(lightThemeIndex);
+    expect(uiVersionIndex).toBeLessThan(appearanceBranchIndex);
+    expect(macWindowIndex).toBeGreaterThan(uiVersionIndex);
+    expect(appSource).toContain("badge: '默认'");
+    expect(appSource).toContain("badge: 'Beta'");
+    expect(appSource).toContain("onClick={() => setAppearance({ uiVersion: item.key as 'legacy' | 'v2' })}");
+    expect(appSource).toContain('新版 UI 仍在 Beta');
+    expect(appSource).toContain('Windows、macOS 与 Linux 均可切换');
+  });
+
+  it('uses the card-style v2 switch from the redesign instead of the segmented pill', () => {
+    const uiVersionIndex = appSource.indexOf('界面版本');
+    const themeModeIndex = appSource.indexOf('主题模式', uiVersionIndex);
+    const uiVersionBlock = appSource.slice(uiVersionIndex, themeModeIndex);
+
+    expect(uiVersionBlock).toContain('NEW');
+    expect(uiVersionBlock).toContain("gridTemplateColumns: 'repeat(2, minmax(0, 1fr))'");
+    expect(uiVersionBlock).toContain("label: '旧版 UI'");
+    expect(uiVersionBlock).toContain("label: '新版 UI'");
+    expect(uiVersionBlock).toContain('CheckOutlined');
+    expect(uiVersionBlock).not.toContain('<Segmented');
+  });
+});