fix(release): align supported candidate matrix

[ZSeanYves]

Summary

• install exact MoonBit dependencies in every isolated release candidate job before frozen builds
• update setup-moonbit to the official v1.23 immutable commit
• remove the unsupported macOS Intel candidate and document the supported Native matrix

Evidence

• candidate run 31674990173 passed source validation but exposed cold dependency installation and official macOS Intel toolchain removal
• official setup-moonbit v1.23 release notes confirm Intel macOS support was dropped
• serial tools/check_phase11.sh passes
• commit hook full gate: 303 Native tests and 298 wasm1 tests
• workflow YAML, ShellCheck, Python compile and immutable action-pin audits pass

Publication boundary

This PR does not publish packages, create releases, or create/push tags.