feat: add error boundary to prevent white-screen crashes

Wraps the entire app in an ErrorBoundary that shows a friendly
error message with reload button instead of crashing to white.

frontend/src/components/ErrorBoundary.tsx

@@ -0,0 +1,44 @@
+import { Component, type ErrorInfo, type ReactNode } from 'react';
+
+interface Props {
+  children: ReactNode;
+}
+
+interface State {
+  hasError: boolean;
+  error: Error | null;
+}
+
+export class ErrorBoundary extends Component<Props, State> {
+  state: State = { hasError: false, error: null };
+
+  static getDerivedStateFromError(error: Error): State {
+    return { hasError: true, error };
+  }
+
+  componentDidCatch(error: Error, errorInfo: ErrorInfo) {
+    console.error('ErrorBoundary caught:', error, errorInfo);
+  }
+
+  render() {
+    if (this.state.hasError) {
+      return (
+        <div className="flex items-center justify-center min-h-screen bg-background">
+          <div className="text-center p-8 max-w-md">
+            <h1 className="text-xl font-bold mb-2 text-foreground">Something went wrong</h1>
+            <p className="text-muted-foreground mb-4 text-sm">
+              {this.state.error?.message ?? 'An unexpected error occurred.'}
+            </p>
+            <button
+              onClick={() => window.location.reload()}
+              className="px-4 py-2 bg-primary text-primary-foreground rounded-md text-sm font-medium hover:bg-primary/90 transition-colors"
+            >
+              Reload Page
+            </button>
+          </div>
+        </div>
+      );
+    }
+    return this.props.children;
+  }
+}

frontend/src/main.tsx

@@ -2,6 +2,7 @@ import { StrictMode } from 'react';
 import { createRoot } from 'react-dom/client';
 import { BrowserRouter } from 'react-router-dom';
 import App from './App.tsx';
+import { ErrorBoundary } from './components/ErrorBoundary.tsx';
 import './index.css';
 
 import { AuthProvider } from "react-oidc-context";
@@ -12,10 +13,12 @@ startCollector();
 
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
-    <AuthProvider {...oidcConfig}>
-      <BrowserRouter>
-        <App />
-      </BrowserRouter>
-    </AuthProvider>
+    <ErrorBoundary>
+      <AuthProvider {...oidcConfig}>
+        <BrowserRouter>
+          <App />
+        </BrowserRouter>
+      </AuthProvider>
+    </ErrorBoundary>
   </StrictMode>,
 )