ci: install Playwright chromium for the storybook vitest project; deterministic in-flight test

- CI runs the @vitest/browser-playwright (storybook) project, which needs the
  chromium browser downloaded — add 'playwright install --with-deps chromium'.
- object-new-page in-flight test held the create mutation open with a 50ms
  delay and raced the pending-state assertion (failed under CI timing); gate it
  on a promise released only after asserting 'saving…', so it's deterministic.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yaml

@@ -26,6 +26,7 @@ jobs:
       - run: pnpm install --frozen-lockfile
       - run: pnpm typecheck
       - run: pnpm lint
+      - run: pnpm exec playwright install --with-deps chromium
       - run: pnpm test
       - run: pnpm build
       - run: pnpm check:size