Ship first agent skill: map a field between two hosted standards

[jonsykescherre]

skills/ is documented but empty. This ships the first real artifact of deliverable #3 (AI skills and agent definitions).

What: A SKILL.md that packages the context an agent needs to map a field from one hosted standard to another using CORA crosswalks.

Deliverables:

• SKILL.md following the directory shape in skills/README.md
• Inputs/outputs and a worked prompt example (can reference the worked example in Add first worked example: MITS → REDI record walkthrough #58)
• Note which crosswalk files the skill reads

Why: First tangible skill artifact; sets the pattern for future per-standard and per-crosswalk skills.

Scope: ~1 hour. Depends loosely on the worked example in #58.