feat(check): every skill states when it stops and hands back

Implements #5's decision. The hard part was #37's, not #5's: which skills need
an escalation rule? A hardcoded list rots, sniffing the prose for "does this
write anything" is unfalsifiable, and a frontmatter flag is the option #5
rejected wearing a hat.

So there is no acting set. Every skill answers the question, and a read-only one
answers it in a line. That turns an absence into a claim someone can disagree
with, which is the whole point — "this skill never hands back" is a design
decision worth stating, and today it was indistinguishable from nobody having
thought about it.

Eleven written here, all advisory or read-only, where the honest answer is short
and the value is in being specific rather than generic. `cognitive-load` stops
when the metric disagrees with the people reading the code, because that is
evidence about the metric. `test-design` stops when the tests are fine and the
design under test is what makes them awkward. `code-review` stops when the diff
is big enough that a review would be a skim, and says so rather than producing
confident coverage of a fraction.

The remaining thirty are the acting set — writes, dispatches, credentials,
releases — and each needs a rule someone thought about rather than a rote
paragraph, so they sit in bin/escalation-pending.txt. That list only shrinks,
and it is self-cleaning: a listed skill that HAS a section fails the gate, so an
exemption cannot outlive its reason. Mutation-verified both ways.

Six test cases including the stale-entry case, because an exemption for a skill
that no longer exists is how a gate quietly stops covering something.

Refs #37, closes the mechanism half
Bump-Type: minor

skills/cad-babysit/SKILL.md

@@ -258,3 +258,13 @@ decide
 - `mathias/cad-atlas#11` renders the same `cad stuck` output as a pipeline overlay — read that
   instead of this skill's text output when a visual "where is everything stuck" view is wanted
   over working one row in depth.
+
+## Escalation
+
+Read-only by construction, and the Iron Laws above are the escalation rule: never close
+an issue, never dispatch, never write a label. Everything that is the operator's call
+leaves as a `DECISION NEEDED` block (question / options / recommendation / blocks).
+
+Stop and hand back when: the stuck queue is empty; a diagnosis needs a write you are not
+allowed to make; or two runs in a row produce the same finding, which means the finding
+is not being acted on and repeating it is noise.