v0.2.0: 全面代码质量优化

- ESLint flat config + Prettier + EditorConfig
- Markdown处理器LRU缓存
- Zustand选择器优化减少重渲染
- CodeMirror Compartment主题热切换
- Preview防抖(150ms) + IndexedDB去抖(500ms)
- 组件拆分: App.tsx 310→104行, Sidebar.tsx 244→90行
- 统一错误处理 errorHandler.ts
- ConfirmDialog替代原生confirm
- LoadingSpinner加载状态
- Toast多条堆叠+类型区分
- 可访问性增强(ARIA属性、键盘导航)
- Vitest测试框架(78个测试用例)
- Git hooks(husky + lint-staged)
- 项目文档(README.md, CONTRIBUTING.md)

src/renderer/components/AboutDialog/AboutDialog.tsx

@@ -0,0 +1,55 @@
+import React from 'react'
+import { AppIcon, Gitee } from '../Icons'
+
+const APP_VERSION = 'v0.2.0'
+
+interface AboutDialogProps {
+  onClose: () => void
+}
+
+export const AboutDialog = React.memo(function AboutDialog({ onClose }: AboutDialogProps) {
+  const handleLinkClick = (e: React.MouseEvent<HTMLAnchorElement>): void => {
+    e.preventDefault()
+    if (window.electronAPI?.openExternal) {
+      window.electronAPI.openExternal('https://gitee.com/thzxx/MarkLite')
+    } else {
+      window.open('https://gitee.com/thzxx/MarkLite', '_blank')
+    }
+  }
+
+  return (
+    <div className="about-overlay" onClick={onClose} role="dialog" aria-modal="true" aria-label="关于 MarkLite">
+      <div className="about-dialog" onClick={(e: React.MouseEvent) => e.stopPropagation()}>
+        <div className="about-header">
+          <AppIcon size={64} />
+          <h2>MarkLite</h2>
+          <span className="about-version">{APP_VERSION}</span>
+        </div>
+        <div className="about-body">
+          <p>一款轻量级的 Windows 本地 Markdown 编辑器</p>
+          <div className="about-features">
+            <span>多标签页</span>
+            <span>实时预览</span>
+            <span>代码高亮</span>
+            <span>暗色主题</span>
+            <span>拖拽打开</span>
+            <span>搜索替换</span>
+            <span>文件树</span>
+            <span>状态持久化</span>
+          </div>
+        </div>
+        <div className="about-footer">
+          <a className="about-link" href="#" onClick={handleLinkClick}>
+            <Gitee size={16} />
+            <span>gitee.com/thzxx/MarkLite</span>
+          </a>
+          <p>基于 Electron + React + TypeScript 构建</p>
+          <p className="about-copyright">© 2026 thzxx</p>
+        </div>
+        <button className="about-close-btn" onClick={onClose}>关闭</button>
+      </div>
+    </div>
+  )
+})
+
+AboutDialog.displayName = 'AboutDialog'