Feature: Global error boundary and 404 page

[FadyGergesRezk]

Add global error handling so uncaught render errors and unknown routes degrade gracefully instead of crashing the app.

Priority: P0

Tasks

• Add a GlobalErrorBoundary class component in src/app/ErrorBoundary.tsx that catches uncaught render errors, logs them to the console, and renders a user-facing fallback with a "Go home" action
• Wrap the app root in GlobalErrorBoundary (outside QueryClientProvider so provider errors are also caught)
• Add a NotFoundPage component for unmatched routes with a clear message and a link back to /members
• Add a catch-all path="*" route in AppRouter.tsx that renders NotFoundPage
• Configure TanStack Query QueryClient to not retry on 4xx errors (already noted in Feature: Client foundation — Zustand, daisyUI, and app shell #43 but must be verified here)

Acceptance criteria

• Navigating to an unknown URL renders the 404 page instead of a blank screen
• A thrown render error inside any page renders the error boundary fallback instead of crashing the whole app
• The "Go home" action in the error boundary navigates back to /members
• Error boundary fallback provides an explicit reset/retry action