feat(security): add global error boundary for defense in depth

- Adds `ErrorBoundary` component to catch unhandled React exceptions
- Prevents UI crashes (White Screen of Death)
- Ensures stack traces are not leaked to the user (Security Enhancement)
- Wraps `App` in `main.tsx`
- Adds tests verifying fallback UI and absence of error details in DOM

Co-authored-by: ragusa-it <196988693+ragusa-it@users.noreply.github.com>

src/main.tsx

@@ -1,9 +1,12 @@
 import { StrictMode } from 'react';
 import { createRoot } from 'react-dom/client';
 import { App } from './App';
+import { ErrorBoundary } from './components/layout';
 
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
-    <App />
+    <ErrorBoundary>
+      <App />
+    </ErrorBoundary>
   </StrictMode>
 );