ErrorBoundary追加: アプリ全体のエラーハンドリング強化

- ErrorBoundaryコンポーネントを新規作成（App全体・ページ個別の二重ガード）
- ImportPage: 日付フィールドのundefined時にlocaleCompareが落ちる問題を修正

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/App.tsx

@@ -6,6 +6,7 @@ import JournalPage from './components/JournalPage';
 import LedgerPage from './components/LedgerPage';
 import BalanceSheetPage from './components/BalanceSheetPage';
 import SettingsPage from './components/SettingsPage';
+import { ErrorBoundary } from './components/ErrorBoundary';
 
 export default function App() {
   const { currentPage } = useStore();
@@ -22,8 +23,12 @@ export default function App() {
   };
 
   return (
-    <Layout>
-      {renderPage()}
-    </Layout>
+    <ErrorBoundary>
+      <Layout>
+        <ErrorBoundary>
+          {renderPage()}
+        </ErrorBoundary>
+      </Layout>
+    </ErrorBoundary>
   );
 }

src/components/ErrorBoundary.tsx

@@ -0,0 +1,46 @@
+import { Component, type ErrorInfo, type ReactNode } from 'react';
+
+interface Props {
+  children: ReactNode;
+}
+
+interface State {
+  hasError: boolean;
+  error?: Error;
+}
+
+export class ErrorBoundary extends Component<Props, State> {
+  constructor(props: Props) {
+    super(props);
+    this.state = { hasError: false };
+  }
+
+  static getDerivedStateFromError(error: Error): State {
+    return { hasError: true, error };
+  }
+
+  componentDidCatch(error: Error, info: ErrorInfo) {
+    console.error('[ErrorBoundary] Caught error:', error, info.componentStack);
+  }
+
+  render() {
+    if (this.state.hasError) {
+      return (
+        <div className="flex flex-col items-center justify-center h-screen text-slate-400 p-8 bg-slate-900">
+          <p className="text-5xl mb-4">⚠️</p>
+          <p className="text-lg font-semibold text-slate-300 mb-2">エラーが発生しました</p>
+          <p className="text-sm text-slate-500 mb-6 max-w-md text-center break-all">
+            {this.state.error?.message}
+          </p>
+          <button
+            onClick={() => this.setState({ hasError: false })}
+            className="px-4 py-2 bg-indigo-600 text-white rounded-md text-sm hover:bg-indigo-700"
+          >
+            再試行
+          </button>
+        </div>
+      );
+    }
+    return this.props.children;
+  }
+}

src/components/ImportPage.tsx

@@ -78,7 +78,7 @@ export default function ImportPage() {
 
   // 振替としてスキップされた取引（振替=1 のrawRecords）
   const skippedTransfers = useMemo(() =>
-    rawRecords.filter(r => r.振替 === '1' && r.ID).sort((a, b) => b.日付.localeCompare(a.日付)),
+    rawRecords.filter(r => r.振替 === '1' && r.ID).sort((a, b) => (b.日付 ?? '').localeCompare(a.日付 ?? '')),
     [rawRecords]
   );