test: correct cross-platform CI fixtures and name stalled tests

[VolkerChristian]

Issue 2 — approved bounded fixture corrections and named-test safety net

This is not a claim that AutoTalk CI is fixed. Run #6: https://github.com/SNodeC/AutoTalk/actions/runs/38188305193.

Root cause and boundary

The fake vLLM worker fixture patched runtime.speech_backend but not the separate binding imported by services. On macOS the real mlx selection therefore discarded the fixture's vLLM progress messages. Patch both existing consumer bindings. The QObject lifetime fixture tested unsupported native capture on macOS despite stubbing capture start; model Linux within this fixture only and explicitly retain/test the real unsupported-platform guard for macOS and Windows.

Add the owner-approved pytest-timeout 2.4.0 safety net (300 seconds, thread method) so future test hangs fail with a named test. No job timeout extension, additional skips, weakened assertions, product-code changes or workflow changes.

Verification

• Full local Linux/offscreen suite, Python 3.12 / Qt 6.11.2: 569 passed, 1 failed, 8 deselected, 126.32 seconds. The remaining test_real_sigint_runs_cleanup_and_reaps_speech_child subprocess exceeds its existing 10-second wait after SIGINT. That independent defect remains unresolved; its limit was not changed.
• Focused backend-progress and screen-capture tests with the services binding initially modeled as macOS/mlx: 26 passed, 3.57 seconds. This is a modeled backend regression, not native macOS certification.
• docs-audit --repo .: 0 violations.
• git diff --check: passed.

The one-hour Ubuntu/Windows CI hang was not reproduced locally and is not claimed resolved. No healthy all-platform runtime established. No GitHub CI dispatch for this branch; CI remains manual-only.

Accounting

Production application code: 0 lines changed. Configuration: +3/-1. Tests: +10/-0. No licences, tags, settings or defaults changed.

[VolkerChristian]

Closing as superseded by the CI fixes merged in PR #11. CI is now green on Linux, Windows, and macOS. The remaining test coverage and timeout changes in this PR are optional and are not required for the CI repair.