test(storage): cover Windows session bundle metadata

[liugddx]

Summary

• pin the canonical Windows Session Bundle TAR and archive digests
• validate hydrated file modes using Node's synthesized Windows metadata
• retain the existing POSIX executable-bit and golden archive assertions

Root cause

Windows does not represent POSIX executable bits. The fixture's chmod(0755) therefore leaves run.sh non-executable in source metadata, so the codec correctly packs it as 0644. Node also reports hydrated regular files with a synthesized 0666 mode on Windows. The previous test assumed POSIX metadata on every host.

This change does not infer executability from file extensions and does not alter the Session Bundle codec contract.

Validation

• deterministic pack, inspect, and atomic hydrate test: four consecutive passes on Windows
• npm run build
• npm run typecheck
• Biome check
• git diff --check

Two unrelated symlink tests require Windows symbolic-link privileges on this local machine; they are not the Session Bundle failure recorded by the Windows CI baseline.

Relates to #2142.