gemini-nexus/openspec/changes/add-multiarch-release-artifacts/tasks.md

1. Implementation

• 1.1 Update the release workflow matrix to add Linux arm64 builds and split build steps by architecture.
• 1.2 Add macOS universal build flow (merge app bundles before generating universal dmg).
• 1.3 Introduce Windows MSI maker and required dependencies, and generate MSI in the Windows job.
• 1.4 Extend postMake artifact renaming and architecture mapping logic to generate SHA-256 checksum files.
• 1.5 Update release attachments and artifact inventory documentation (if needed).
• 1.6 Verify CI outputs for Linux arm64, macOS universal, and Windows MSI.