Add demo mode support with MSW integration and documentation

- Integrated Mock Service Worker (MSW) for frontend-only demo mode, allowing API call interception without requiring a backend.
- Added `DemoModeBanner` component to indicate active demo mode and display demo credentials.
- Enhanced configuration with `DEMO_MODE` flag and demo credentials for user and admin access.
- Updated ESLint configuration to exclude MSW-related files from linting and coverage.
- Created comprehensive `DEMO_MODE.md` documentation for setup and usage guidelines, including deployment instructions and troubleshooting.
- Updated package dependencies to include MSW and related libraries.

CLAUDE.md

@@ -173,6 +173,17 @@ with patch.object(session, 'commit', side_effect=mock_commit):
 - E2E: Use `npm run test:e2e:debug` for step-by-step debugging
 - Check logs: Backend has detailed error logging
 
+**Demo Mode (Frontend-Only Showcase):**
+- Enable: `echo "NEXT_PUBLIC_DEMO_MODE=true" > frontend/.env.local`
+- Uses MSW (Mock Service Worker) to intercept API calls in browser
+- Zero backend required - perfect for Vercel deployments
+- Demo credentials:
+  - User: `demo@example.com` / `DemoPass123`
+  - Admin: `admin@example.com` / `AdminPass123`
+- **Safe**: MSW never runs during tests (Jest or Playwright)
+- **Coverage**: Mock files excluded from linting and coverage
+- **Documentation**: `frontend/docs/DEMO_MODE.md` for complete guide
+
 ### Tool Usage Preferences
 
 **Prefer specialized tools over bash:**