Prevent Qt aborts while applying settings

[luinbytes]

Summary

• keep Python exceptions inside the Settings Apply signal boundary so PyQt does not terminate through qFatal
• persist selected settings before refreshing Qt and audio objects, allowing restart recovery
• add a subprocess regression that clicks the real Apply button, injects a runtime failure, verifies the process survives, and verifies sound-off persists
• gate release packaging on the test suite and restrict publication to v* tags

Evidence

• Before fix: the regression process aborted twice with exit 134 after the Apply callback raised
• Local: python -m unittest discover tests -v -> 23 tests, 2 expected skips
• Windows preflight: PyQt5 5.15.10 / Qt 5.15.2, 23 tests with the Apply regression passing, then successful BongoCat-windows-x64.exe build
• Full preflight: Windows, macOS, and Linux tests and package builds passed in run 33548715273

Addresses #10. The issue stays open pending reporter validation of the packaged Windows release.

[luinbytes]

Merged as 4df56ca873ffad68e64576547b4f61a1cf5b8353.

Verification:

• Red repro before the fix: the real Apply button aborted the Qt subprocess with exit 134 twice when a runtime operation raised.
• Local: QT_QPA_PLATFORM=offscreen python -m unittest discover tests -v -> 23 tests passed, 2 expected skips.
• Workflow validation: actionlint .github/workflows/release.yml passed.
• Windows-latest preflight used PyQt5 5.15.10 / Qt 5.15.2; the Apply regression passed, all 23 tests passed with 1 expected skip, and BongoCat-windows-x64.exe built successfully.
• macOS and Linux tests and package builds also passed.
• Preflight run: https://github.com/luinbytes/bongocat/actions/runs/33548715273

Caveat: issue #10 remains open until the reporter validates the packaged candidate on Windows 11 24H2.