Add browser smoke tests for the page

[lesnik512]

Adds browser smoke tests for the page, which until now had only the translation-key checks in tests/test_page.py. Each page change so far was checked by hand in a browser.

tests/test_browser.py runs the real collect in-process against the existing respx scenario with Jira, writes the site to a temp directory, serves it on a free local port, and drives it in headless Chromium through pytest-playwright. Every test also fails on a console error or an uncaught page error.

• the page lists team/svc, and the issue list puts Done first (SHOP-9, then SHOP-12);
• ticking SHOP-12 picks 1.2.0, shows for SHOP-12, writes #issues=SHOP-12&team/svc=1.2.0, and a reload keeps the pick and the tick;
• picking 1.1.0 by hand shows its chip, closes the service, and updates the address;
• switching to Russian renders Состав релиза with no {placeholder} left.

pytest-playwright>=0.10 joins the dev group, so the module imports everywhere; its greenlet dependency has wheels for 3.14t, so the free-threaded jobs still install. The tests carry a smoke marker that addopts deselects, so just test, just test-ci, the floors and pytest matrices, and the coverage gate do not need a browser. just test-smoke installs Chromium when missing and runs only them, and a new smoke job runs that on 3.13 with playwright install --with-deps chromium. The browser download, about 100 MB, is not cached yet.

Playwright for Python keeps the repo free of Node. AGENTS.md now points to the smoke tests instead of saying the page has none.

Locally: just test-smoke passes (4 tests, about 3.5 s), and all four fail when a JavaScript error is injected into the page. just test-ci (140 passed, 4 deselected, 100% coverage) and just lint-ci pass.