ci(skill-check): scan the docs a contributor reads

The check asserts that every make target named in a doc exists, and its
scanned set was .pi/ plus CLAUDE.md.  Since #50, CONTRIBUTING.md is the
document a *human* goes to for a build command, and it names 21 targets
that nothing verified; README.md names none today and is in for the same
reason.  The script's own header sentence is the argument — a renamed
target sends a person off the same cliff it sends an agent off.

The file list is now one `docs` variable used twice, because the failure
message carried a second copy of it and a second list is a second thing
to forget.  The `[ -d .pi ]` guard went with it: gating the whole run on
.pi/ would make the human-facing half conditional on the agent-facing
one, and an empty list is the same "nothing to scan" exit without the
coupling.

The lefthook glob is that scanned set now rather than
{Makefile,.pi/**/*.md} — #220's smaller half, and it did not fire on
CLAUDE.md either, which the script had read for months.

Verified by planting a bad target rather than by reading the diff: both
matched forms in each of the four scanned surfaces, each naming the
right file; the same two plants pass on the pre-change script; unfenced
prose still does not match; and the hook fires on a staged
CONTRIBUTING.md under the new glob where the old one skipped it.  The
count is unchanged at 47 — the set is a union — so coverage is the only
thing that moved.

Closes #220

scripts/skill-check.sh

@@ -14,6 +14,11 @@
 # missing: CLAUDE.md names 27 targets and nothing verified one of them,
 # so the file the agents trust most was the file least checked.
 #
+# README.md and CONTRIBUTING.md are in it too, and the header sentence
+# above is why: a person who has *not* read the Makefile goes looking in
+# the contributor-facing doc, so a renamed target sends them off the
+# same cliff it sends an agent off.  CONTRIBUTING.md names 21 targets.
+#
 # **AGENTS.md is a symlink to CLAUDE.md.**  This repo is worked on by
 # two agent harnesses that read different files by convention — Claude
 # Code reads CLAUDE.md, others read AGENTS.md — and two harnesses
@@ -43,7 +48,19 @@ if [ -e AGENTS.md ] || [ -L AGENTS.md ]; then
 	fi
 fi
 
-[ -d .pi ] || exit 0
+# The scan is over the docs that are actually there: a checkout without
+# .pi/ still has README.md and CONTRIBUTING.md to check, and gating the
+# whole run on .pi/ would have made the human-facing half conditional on
+# the agent-facing one.  This list is used twice — once to read the
+# mentions out and once to say which file a missing target came from —
+# because a second list is a second thing to forget.
+# `ls` exits non-zero when *any* of its arguments is missing while still
+# printing the ones that are there, and under `set -e` that would sink
+# the assignment rather than scanning what exists, so swallow it.
+docs="$({ find .pi -name '*.md' 2>/dev/null
+	ls CLAUDE.md README.md CONTRIBUTING.md 2>/dev/null || true; })"
+
+[ -n "$docs" ] || exit 0
 
 # `make -pq` prints the database including every rule, without running
 # anything.  It exits non-zero when a target is out of date, and under
@@ -68,7 +85,7 @@ targets="$({ make -pqRr 2>/dev/null || true; } |
 # AGENTS.md is deliberately not in this list: it is a symlink to
 # CLAUDE.md, asserted above, so scanning it would report every failure
 # twice under two names.
-mentioned="$({ find .pi -name '*.md' 2>/dev/null; echo CLAUDE.md; } |
+mentioned="$(printf '%s\n' "$docs" |
 	xargs awk '
 		FNR == 1 { fence = 0 }
 		/^```/   { fence = !fence; next }
@@ -93,10 +110,10 @@ for t in $mentioned; do
 done
 
 if [ -n "$missing" ]; then
-	echo "skill-check: the agent docs name make targets that do not exist:" >&2
+	echo "skill-check: the docs name make targets that do not exist:" >&2
 	for t in $missing; do
 		echo "  make $t" >&2
-		grep -rln "make $t" .pi CLAUDE.md --include='*.md' | sed 's/^/      /' >&2
+		printf '%s\n' "$docs" | xargs grep -ln "make $t" | sed 's/^/      /' >&2
 	done
 	echo "Fix the docs, or restore the target." >&2
 	exit 1