feat(web): add mobile viewport testing and Tailwind lint rules
Add eslint-plugin-better-tailwindcss for Tailwind v4 correctness
checks (conflicting classes, duplicate classes, unknown classes).
Add Playwright mobile audit test suite that runs against staging at
375px viewport, checking horizontal overflow and a11y violations.
Ignore playwright-report/ and test-results/ from both ESLint and git.
Relates to barazo-forum/barazo-workspace#69