feat(frontend): add ErrorBoundary component

Add React ErrorBoundary component for catching and handling
render errors in component trees with fallback UI.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/components/common/ErrorBoundary.tsx

@@ -0,0 +1,158 @@
+/**
+ * Error Boundary Component
+ *
+ * Catches JavaScript errors in child component tree and displays fallback UI.
+ * Prevents the entire app from crashing due to component-level errors.
+ *
+ * @see https://react.dev/reference/react/Component#catching-rendering-errors-with-an-error-boundary
+ */
+
+'use client';
+
+import { Component, type ReactNode } from 'react';
+import { AlertTriangle, RefreshCw } from 'lucide-react';
+import { Button } from '@/components/ui/button';
+import {
+  Card,
+  CardContent,
+  CardDescription,
+  CardHeader,
+  CardTitle,
+} from '@/components/ui/card';
+
+// ============================================================================
+// Types
+// ============================================================================
+
+interface ErrorBoundaryProps {
+  /** Child components to render */
+  children: ReactNode;
+  /** Optional fallback component to render on error */
+  fallback?: ReactNode;
+  /** Optional callback when error occurs */
+  onError?: (error: Error, errorInfo: React.ErrorInfo) => void;
+  /** Whether to show reset button (default: true) */
+  showReset?: boolean;
+}
+
+interface ErrorBoundaryState {
+  hasError: boolean;
+  error: Error | null;
+}
+
+// ============================================================================
+// Default Fallback Component
+// ============================================================================
+
+interface DefaultFallbackProps {
+  error: Error | null;
+  onReset: () => void;
+  showReset: boolean;
+}
+
+function DefaultFallback({ error, onReset, showReset }: DefaultFallbackProps) {
+  return (
+    <Card className="m-4 border-destructive/50 bg-destructive/5">
+      <CardHeader>
+        <CardTitle className="flex items-center gap-2 text-destructive">
+          <AlertTriangle className="h-5 w-5" aria-hidden="true" />
+          Something went wrong
+        </CardTitle>
+        <CardDescription>
+          An unexpected error occurred. Please try again or contact support if
+          the problem persists.
+        </CardDescription>
+      </CardHeader>
+      <CardContent>
+        {error && (
+          <div className="mb-4 rounded-md bg-muted p-3">
+            <p className="font-mono text-sm text-muted-foreground">
+              {error.message}
+            </p>
+          </div>
+        )}
+        {showReset && (
+          <Button
+            variant="outline"
+            size="sm"
+            onClick={onReset}
+            className="gap-2"
+          >
+            <RefreshCw className="h-4 w-4" aria-hidden="true" />
+            Try again
+          </Button>
+        )}
+      </CardContent>
+    </Card>
+  );
+}
+
+// ============================================================================
+// Error Boundary Component
+// ============================================================================
+
+/**
+ * Error boundary for catching and handling render errors in React components.
+ *
+ * @example
+ * ```tsx
+ * <ErrorBoundary onError={(error) => logError(error)}>
+ *   <MyComponent />
+ * </ErrorBoundary>
+ * ```
+ *
+ * @example With custom fallback
+ * ```tsx
+ * <ErrorBoundary fallback={<CustomErrorUI />}>
+ *   <MyComponent />
+ * </ErrorBoundary>
+ * ```
+ */
+export class ErrorBoundary extends Component<
+  ErrorBoundaryProps,
+  ErrorBoundaryState
+> {
+  constructor(props: ErrorBoundaryProps) {
+    super(props);
+    this.state = { hasError: false, error: null };
+  }
+
+  static getDerivedStateFromError(error: Error): ErrorBoundaryState {
+    return { hasError: true, error };
+  }
+
+  componentDidCatch(error: Error, errorInfo: React.ErrorInfo): void {
+    // Log error to console in development
+    console.error('ErrorBoundary caught an error:', error, errorInfo);
+
+    // Call optional error callback
+    this.props.onError?.(error, errorInfo);
+  }
+
+  handleReset = (): void => {
+    this.setState({ hasError: false, error: null });
+  };
+
+  render(): ReactNode {
+    const { hasError, error } = this.state;
+    const { children, fallback, showReset = true } = this.props;
+
+    if (hasError) {
+      if (fallback) {
+        return fallback;
+      }
+
+      return (
+        <DefaultFallback
+          error={error}
+          onReset={this.handleReset}
+          showReset={showReset}
+        />
+      );
+    }
+
+    return children;
+  }
+}
+
+export default ErrorBoundary;

frontend/src/components/common/index.ts

@@ -1,4 +1,4 @@
 // Common reusable components
 // Examples: LoadingSpinner, ErrorBoundary, ConfirmDialog, etc.
 
-export {};
+export { ErrorBoundary } from './ErrorBoundary';