Build macOS release artifacts in matrix and publish in follow-up job

- remove manual `arch` workflow input and build `arm64` + `x64` via matrix
- split release flow into `build-macos` and `publish-release` jobs
- download merged artifacts before creating the GitHub release
c2a588fd02Julius Marminge committed on 2/28/2026, 5:33:34 AMparent249cf8c
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