Move playwright install to commands_pre

[ksy36]

From this error it looks like running uv run --extra=dev playwright install --with-deps chromium firefox, in CI installs browsers matching the playwright version pinned in uv.lock (playwright firefox v1509):

Firefox 146.0.1 (playwright firefox v1509) downloaded to /home/runner/.cache/ms-playwright/firefox-1509

But tox is installing a newer playwright version, so can't locate the browsers that were just installed:

        except Exception as error:
>           raise rewrite_error(error, f"{parsed_st['apiName']}: {error}") from None
E           playwright._impl._errors.Error: BrowserType.launch: Executable doesn't exist at /home/runner/.cache/ms-playwright/firefox-1511/firefox/firefox

Moving the browser install to commands_pre so it runs inside tox virtualenv seems to help.