Build 10 layer scaffolding for skills evaluation

[reidbaker]

https://x.com/i/status/2046876981711769720

This the dart_skills_lint repo should have at least 2 skills before implementing this. Might be better to try it against a larger skills repo first like kevmoo/dash_skills.

[reidbaker-agent]

Moved to google/skills_lint.dart#81, which maps each of the 10 layers to what exists and what is missing.