ci(library): run the headless app block's component tests

`pnpm --filter library test` uses the Node test runner, so the block's
Vitest suite that arrived with headless-app-tanstack was not covered by
the library checks workflow.

test:headless-tools is still not wired up: it shells out to `deno check`
and needs a Deno toolchain in the runner.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.github/workflows/library-tests.yml

@@ -47,6 +47,8 @@ jobs:
 
       - run: pnpm install --frozen-lockfile
       - run: pnpm --filter library test
+      # The block's component tests run under Vitest, so `test` does not cover them.
+      - run: pnpm --filter library test:headless-app
       - name: Check generated registry
         run: |
           registry_changes="$(git status --porcelain --untracked-files=all -- apps/ui-library/public/r apps/ui-library/__registry__)"