ci(vm): remove remaining EKS release assumptions

[jtoelke2]

Summary

Follow up #1186 by removing remaining EKS-specific assumptions from VM/release-adjacent workflows.

Related Issue

Related to OS-49 (Linear). Follows #1186.

Changes

• Move release-canary install-dev and RPM packaging jobs from old build-amd64/build-arm64 labels to shared CPU runner labels.
• Build the macOS driver VM supervisor bundle in a separate arm64 job on shared runners and download it in the macOS packaging job.
• Use local Buildx for the macOS driver VM image build and remove the unused VM SCCACHE memcached environment path.

Testing

• Workflow YAML parses for changed workflow files
• git diff --check origin/main...HEAD
• Targeted grep verified old labels/remote BuildKit/sccache/supervisor-output paths are absent from changed workflows
• mise run pre-commit passes

mise run pre-commit was run on this branch and failed on pre-existing/unrelated local issues: markdownlint scans untracked .codex-learning/*.md, and Rust unit test ssh::tests::launch_editor_returns_friendly_error_when_binary_missing still fails. Rust check, clippy, fmt, Python checks/tests, Helm lint, license check, and Mermaid lint completed before the aggregate failure.

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (not applicable: workflow-only follow-up to ci(vm): cleanup vm build infra #1186)