Add playwright.config.ts with webServer configured to run build and
preview on port 4173. Add e2e/smoke.spec.ts with 4 smoke tests:
rel=me anchor presence, all identity links in HTML, canvas and HUD
visibility, and reduced motion fallback rendering.
Restructure App.tsx to render Scroller outside #demo div to fix
selector ambiguity in e2e tests. Add test.exclude to vite.config.ts
to prevent vitest from running playwright tests.
L'électron rare