ci: restore required test status context

[timeleft--]

Branch protection requires a test status, while the matrix job now emits only test (0.28.0) and test (0.45.1). Clean pull requests therefore remain blocked after both matrix jobs and review pass.

Add a small aggregate test job that succeeds only when the full JJ matrix succeeds. This restores the existing protected-branch contract without weakening or changing repository protection settings.

Validation: git diff --check; workflow structure reviewed locally. GitHub Actions provides final matrix and aggregate validation on this pull request.

[timeleft--]

Hermes review findings were written locally at /Users/yianaga/Documents/AgenticWork/active/investigations/wisdom-finish-20260907/fava-required-test/.wise-agents/reviews/hermes/20260919T221505Z-fix-required-test-context-findings.md.

API call failed after 3 retries: Codex stream produced no SSE events for 12s after the first parsed event (threshold: 12s)

[yia-mw-agent]

Independent exact-head acceptance of 362e44b: the aggregate job is named exactly test, waits for the full JJ matrix, runs even after failure/cancellation, and exits successfully only when the matrix result is success. Both matrix runs and both aggregate test contexts passed, along with semantic PR and CodeQL checks. This restores the existing protected-branch contract without weakening branch protection.