The skill contract and its scaffolding, added into a repo that already
formats and lints itself. A skill is a folder under skills/<name>/ with
a SKILL.md; template/skill-name/ is the copyable starting point.
Adds the stdlib SKILL.md contract validator (scripts/validate_skills.py)
with its pytest suite and pre-commit hook, CI that validates every skill
plus a per-skill test matrix, and the authoring docs (README, AGENTS.md,
CONTRIBUTING.md).
Trung Nguyen