- Create ErrorBoundary and ModalErrorBoundary components with recovery actions (retry, reload)
- Add error boundary CSS styles with fallback UI styling
- Wrap main dashboard pages (Board, List, Settings, Agents) with PageErrorBoundary in App.tsx
- Wrap all key modals (task detail, planning, subtask breakdown, mission) with ModalErrorBoundary in AppModals.tsx
- Wrap entire App with RootErrorBoundary in main.tsx as final safety net
- Add 11 comprehensive ErrorBoundary tests covering all rendering and error scenarios
