Vitest launches a browser the next step installs

Vitest launches a browser the next step installs Three of the seven unit files run in Vitest's browser mode, so `vitest run` needs Playwright's chromium — and the workflow installed it on the line below. The step died with "Executable doesn't exist at .../chromium_headless_shell" after silently running four files out of seven, so the web gate was reporting a browser it did not have rather than a test that did not pass. Invisible on a laptop, which is the whole shape of this class of bug: the browser is already in `~/.cache/ms-playwright` from some earlier run, so the ordering never mattered locally and the suite passed. The `check:web` task had the same order for the same reason and is fixed with it — a local gate that cannot reproduce a CI failure is not much of a gate.