[vchamarthi]

Adds two checks to check_catalog in tools/validate_skills.py, plus a unittest wired into the Validate workflow. A skills.yaml entry with a misspelt key (for example intel-hw-clas) is now an error, and so is an intel-hw-class outside cpu | gpu | npu | accelerator.

Evidence

• base: vchamarthi/intel-skills main 286055b (same as intel/skills main at fetch time)
• command: python3 -m unittest discover -s tests and python3 tools/validate_skills.py
• before: 2 of 4 new tests fail on the old validator. A misspelt key and intel-hw-class: GPU both produce no error. validate_skills.py exits 0.
• after: 4 of 4 tests pass. validate_skills.py exits 0 on the real catalog, so all 33 current entries conform to the documented keys and classes.

Blast radius

• tools/validate_skills.py: two new error paths in check_catalog, reached only when an entry has a key outside the documented set or a non-empty intel-hw-class outside the four classes.
• tests/test_catalog_fields.py: new, standard library only.
• .github/workflows/validate.yml: one new step running that test.
• No skill content, catalog entry, or schema changes. A future PR adding a new catalog key must add it to CATALOG_KEYS.

Created with Claude Code.