[johnl-amd]

Adds docs/checklist.md: every bar the three graders hold a skill to, in one list.

• A section per grader, in the order they run, each opening with what that grader actually does before listing what it wants.
• The rules are taken from the code rather than restated from the prose: the SKILL.md limits from structure.py, the dataset shape and Tier 0 coverage from datasets.py, the four kinds of behavioral check from engine/scorers.py, the pass mark and the two infrastructure checks from routing_gate.
• The CI section keeps reusable.yml and skill-evals.yml apart and gives the former's full input list. routing_room and infra_paths belong only to the latter, which the current docs make easy to get wrong.
• Notes two things that fail quietly: routing ignores a case's workspace and sends the prompt verbatim, and an error or degraded case counts towards neither side of the bar.
• Linked from the README and from the top of both existing docs.

Closes #9

Verified with skillscope structural --docs '*.md,docs/**/*.md': the 37 internal references across the four markdown files resolve.