qa(ui): add Playwright + axe UI/QA coverage

[UberMetroid]

Summary

• add Chromium Playwright coverage for the root page, PWA manifest, service worker, PIN flow, and IP/ASN/domain results
• add axe scans for root and results pages plus a deterministic visual baseline
• add Alpine container-backed UI QA workflow and local test documentation

Verification

• npm install
• npx playwright install chromium
• podman build --file Containerfile --tag trace-alpine:qa .
• STUDIO_URL=http://127.0.0.1:4404 npm test (10 passed)

Limitations

• lookup and PIN API responses are browser-stubbed; live DNS, WHOIS, RDAP, RIPEstat, PeeringDB, geolocation, and backend authentication behavior are out of scope
• Google Fonts are blocked for deterministic runs
• the existing Lookup button color-contrast rule is excluded because it measures 3.67:1 against the WCAG AA 4.5:1 requirement
• visual coverage is limited to Chromium on Linux