There is no make target or documented extra for the browser smoke test #997

Where: Makefile, pyproject.toml ([project.optional-dependencies], markers), CONTRIBUTING.md, tests/browser/test_web_smoke.py, .github/workflows/browser-smoke.yml.

Current gap: #988 added tests/browser/ and a CI workflow, but a contributor has to read the module docstring to learn that it needs pip install playwright and python -m playwright install chromium. make setup does not install either, make test silently skips the file, and there is no make test-browser. The browser marker is registered but nothing documents it.

Repro:

$ make test 2>&1 | tail -2        # tests/browser is collected and reported as skipped, with no hint why
$ grep -n "browser\|playwright" Makefile CONTRIBUTING.md        # no output

Suggested approach: a browser extra (or a make setup-browser target) that installs Playwright and Chromium, a make test-browser target, one paragraph in CONTRIBUTING.md, and a skip reason that names the command.