test(app): await missing checks validation

[albert20260301]

Fix the CI-only lint failure in the data-app contract test.

The assertion now awaits and captures the rejection explicitly, matching the prior failure assertion in the same test. No production behavior or public API changes.

Validation:

• bun run lint
• bun test src/commands/app/check.test.ts

[albert20260301]

@francoischalifour could you review this?

I picked you because you authored the affected data-app contract test and own the target branch. CI is pending; the review focus is preserving the awaited rejection assertion while resolving the type-aware lint failure.

[albert20260301]

Closing this now-redundant stacked repair: the current target branch already contains the lint-safe assertion and PR #118 has a fully green required workflow.