- 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>