chore: add local Playwright browser testing

[commrelayunit]

Summary

• add Playwright config for local Chromium e2e/browser checks on a stable Vite port
• add npm scripts for e2e, headed, UI, and screenshot-oriented runs
• add an unauthenticated app shell smoke test that captures a screenshot artifact
• document browser install, artifact paths, local overrides, and authenticated visual-test guidance

Notes

• This is a separate branch/PR from Replace toast popups with inline CLI feedback #139 because the setup is generic local browser infrastructure.
• A skipped Quoterm edit-paper Save/Sync feedback scaffold is included for Replace toast popups with inline CLI feedback #139 follow-up once stable authenticated fixture data exists.
• Playwright uses safe placeholder Supabase env for unauthenticated shell tests; no production secrets are required or committed.

Verification

• npx playwright install chromium
• npm run test:e2e -- --project=chromium — 1 passed, 1 skipped
• npm run test — 7 files / 15 tests passed
• npm run lint — passed with existing react-hooks warnings in Dashboard.tsx and VaultDetail.tsx