fix(curator): protect hub skills by frontmatter name

[teknium1]

Salvage of #19460 by @LeonSGP43 onto current main, plus a test follow-up.

Summary

_read_hub_installed_names() returned only hub slug keys (e.g. "getnote"). When a hub-installed skill's SKILL.md name: is non-ASCII (e.g. "Get笔记"), the slug-only set didn't protect it, so hermes curator archive "Get笔记" and other curator operations would treat the hub skill as agent-created and archive it.

Changes

• tools/skill_usage.py: walk each hub lock entry's install_path, resolve under skills/ (with traversal guard), read the SKILL.md name:, and add it to the off-limits set alongside the slug.
• tests/tools/test_skill_usage.py: regression test for the getnote/Get笔记 repro. Test follow-up adds mark_agent_created("my-skill") — the original cherry-picked test predates fix(skills): keep manual skills out of curator #19618/fix(curator): only mark agent-created for background-review sediment #19621, which rewrote list_agent_created_skill_names() to require the created_by: "agent" provenance marker.

Validation

• scripts/run_tests.sh tests/tools/test_skill_usage.py → 40 passed
• E2E with real imports + isolated HERMES_HOME:
  • is_agent_created("Get笔记") → False (was True)
  • is_agent_created("getnote") → False (unchanged)
  • archive_skill("Get笔记") → rejected with "bundled or hub-installed; never archive" (was archived)
  • list_agent_created_skill_names() → excludes hub, includes agent-authored
  • Path traversal guard: install_path: "../../../etc" silently skipped, no crash

Closes #19641, #19293.

Credits: @LeonSGP43 for the fix.