refactor: 抽取 Modal 组件、支持 JSON/CSV 导出、清理冗余代码

- 新增 Modal 组件，消除 3 个 Dialog 中重复的遮罩层/Escape/stopPropagation 代码
- PathEditDialog/HelpDialog/ImportDialog 改用 Modal 包裹
- handleExport 支持 JSON/CSV 两种格式（CSV 导出代码之前存在但从未接线）
- App.tsx 移除冗余的 initDarkMode 后重复设 store 的逻辑
- ErrorBoundary 添加 componentDidCatch 日志和 console.error

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/components/dialogs/HelpDialog.tsx

@@ -1,50 +1,20 @@
-import { useEffect } from 'react';
 import { useTranslation } from 'react-i18next';
+import { Modal } from '@/components/ui/Modal';
 
-interface HelpDialogProps {
-  open: boolean;
-  onClose: () => void;
-}
+interface HelpDialogProps { open: boolean; onClose: () => void; }
 
 export function HelpDialog({ open, onClose }: HelpDialogProps) {
   const { t } = useTranslation();
 
-  useEffect(() => {
-    if (!open) return;
-    const handler = (e: KeyboardEvent) => {
-      if (e.key === 'Escape') onClose();
-    };
-    window.addEventListener('keydown', handler);
-    return () => window.removeEventListener('keydown', handler);
-  }, [open, onClose]);
-
-  if (!open) return null;
-
   return (
-    <div
-      className="fixed inset-0 z-50 flex items-center justify-center"
-      style={{ backgroundColor: 'rgba(0,0,0,0.4)' }}
-      onClick={onClose}
-    >
-      <div
-        className="rounded-lg p-6 max-w-lg"
-        style={{ backgroundColor: 'var(--app-bg)', color: 'var(--app-fg)' }}
-        onClick={(e) => e.stopPropagation()}
-      >
-        <h2 className="text-lg font-semibold mb-4">{t('dialog.helpTitle')}</h2>
-        <pre className="text-sm whitespace-pre-wrap font-sans leading-relaxed">
-          {t('help.content')}
-        </pre>
-        <div className="flex justify-end mt-4">
-          <button
-            className="px-4 py-1.5 text-sm rounded text-white"
-            style={{ backgroundColor: '#2563eb' }}
-            onClick={onClose}
-          >
-            {t('dialog.confirm')}
-          </button>
-        </div>
+    <Modal open={open} onClose={onClose}>
+      <h2 className="text-lg font-semibold mb-4">{t('dialog.helpTitle')}</h2>
+      <pre className="text-sm whitespace-pre-wrap font-sans leading-relaxed max-w-lg">{t('help.content')}</pre>
+      <div className="flex justify-end mt-4">
+        <button className="px-4 py-1.5 text-sm rounded text-white" style={{ backgroundColor: '#2563eb' }} onClick={onClose}>
+          {t('dialog.confirm')}
+        </button>
       </div>
-    </div>
+    </Modal>
   );
 }