fix(skills): handle bytes in bundle content hash

[zhao0112]

Summary

• handle bytes entries in bundle_content_hash() without calling .encode()
• preserve the existing hash behavior for text bundle files
• add a regression test covering mixed bytes and str bundle content

Fixes #13408

Root Cause

bundle_content_hash() assumed every bundle.files[...] value was a str and always called .encode("utf-8"). SkillBundle.files is already typed as Dict[str, Union[str, bytes]], so any bundle containing raw bytes would crash during hermes skills update with AttributeError.

Validation

• /Users/zzl/.hermes/hermes-agent-update-20260421/venv/bin/python -m pytest -o addopts= tests/tools/test_skills_hub.py -q
• /Users/zzl/.hermes/hermes-agent-update-20260421/venv/bin/python -m py_compile tools/skills_hub.py tests/tools/test_skills_hub.py
• git diff --check

[alt-glitch]

Related to #3751 (open) — same bytes-in-bundle-hash fix. Maintainers should pick one.

[alt-glitch]

Related to #3751 (open) — same bytes-in-bundle-hash fix. Maintainers should pick one.