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/LoadingSpinner/LoadingSpinner.tsx

@@ -0,0 +1,70 @@
+import React from 'react'
+
+interface LoadingSpinnerProps {
+  size?: 'small' | 'medium' | 'large'
+  label?: string
+  /** 是否全屏覆盖 */
+  overlay?: boolean
+}
+
+const sizeMap = {
+  small: 16,
+  medium: 24,
+  large: 36
+}
+
+/**
+ * UX-02: 通用加载指示器组件
+ */
+export const LoadingSpinner = React.memo(function LoadingSpinner({
+  size = 'medium',
+  label,
+  overlay = false
+}: LoadingSpinnerProps) {
+  const px = sizeMap[size]
+
+  const spinner = (
+    <div
+      className={`loading-spinner loading-spinner-${size}`}
+      role="status"
+      aria-label={label || '加载中'}
+    >
+      <svg
+        className="loading-spinner-svg"
+        width={px}
+        height={px}
+        viewBox="0 0 24 24"
+        fill="none"
+        xmlns="http://www.w3.org/2000/svg"
+        aria-hidden="true"
+      >
+        <circle
+          cx="12"
+          cy="12"
+          r="10"
+          stroke="currentColor"
+          strokeWidth="3"
+          strokeLinecap="round"
+          opacity="0.2"
+        />
+        <path
+          d="M12 2a10 10 0 0 1 10 10"
+          stroke="currentColor"
+          strokeWidth="3"
+          strokeLinecap="round"
+        />
+      </svg>
+      {label && <span className="loading-spinner-label">{label}</span>}
+    </div>
+  )
+
+  if (!overlay) return spinner
+
+  return (
+    <div className="loading-overlay" aria-busy="true">
+      {spinner}
+    </div>
+  )
+})
+
+LoadingSpinner.displayName = 'LoadingSpinner'