feat: add Design System page + Playwright visual regression tests (PR8)
Design System page (/design-system):
- Showcases all pattern components: SettingsCard, FieldRow, StatusBanner,
EmptyState, IconAction, SectionPage
- Includes Button variants, Input, Select, Switch, Badge primitives
- Each section has data-section attribute for targeted screenshots
Visual regression tests (npm run test:visual):
- Full design system page screenshot
- Individual section screenshots (buttons, status banners, cards, field rows)
- Settings page screenshot
- Uses maxDiffPixelRatio: 0.01 for tight regression detection
Infrastructure:
- Add test:visual script to package.json
- Update playwright.config.ts with screenshot comparison defaults
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
