Adds playwright + pytest-playwright to workspace dev deps, an e2e
pytest marker, and a live_server fixture that boots the Flask app on
an ephemeral port with a temp SQLite DB. addopts default to -m 'not
e2e' so the regular fast suite excludes them; explicit
`pytest -m e2e` runs them. Smoke test confirms the live server is
reachable.
Workspace root pyproject.toml is the right place for the dev deps and
pytest config — l4d2web/pyproject.toml is minimal and has neither.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
