fix: handle bytes in skills bundle content hash

[xiew4589-lang]

Summary

• fix bundle_content_hash() to handle both bytes and str file contents
• prevent hermes skills check from crashing when a skill bundle contains binary assets
• add a regression test covering mixed text + binary bundle contents

Verification

• python -m pytest tests/tools/test_skills_hub.py -q -o 'addopts=' ✅
• hermes skills check ✅
• python -m pytest tests/tools/ -q -o 'addopts=' shows 5 existing unrelated failures
• confirmed the same 5 failures also reproduce on origin/main

Existing unrelated test failures on base branch

• tests/tools/test_file_staleness.py::TestStalenessCheck::test_warning_when_file_modified_externally
• tests/tools/test_file_staleness.py::TestPatchStaleness::test_patch_warns_on_stale_file
• tests/tools/test_send_message_missing_platforms.py::TestSendMatrix::test_success
• tests/tools/test_transcription.py::TestGetProvider::test_explicit_local_no_cloud_fallback
• tests/tools/test_transcription.py::TestGetProvider::test_local_nothing_available

Root cause

bundle_content_hash() assumed every bundle entry was text and called .encode("utf-8") unconditionally. When a skill bundle included binary content already represented as bytes, hermes skills check crashed with:

AttributeError: 'bytes' object has no attribute 'encode'

[teknium1]

Thanks for the contribution, @xiew4589-lang!

Closing this as a duplicate of #2740 (by @Mibayy), which targets the same fix/feature. We're consolidating on that PR for review.

If you want to help push it over the line, please jump in there — or if you think your approach is better for a specific reason that isn't covered in the other PR, let us know and we can reopen.