feat(lint): expand Vale audit prefilter into a broader plugin-content harness

Deferred item from PR #85 review. Per ADR-0013: cherry-picks two low-noise
rules from trialing write-good/alex against the real corpus (VagueQualifier,
SentenceOpenerThereIs) into styles/Kyberforge rather than adopting either
package wholesale (both are tuned for blog prose and were noisy on this
repo's terse, imperative instruction files - see the ADR's rejected-rule
list). Adds a new skill-size-check pre-commit hook enforcing agentskills.io's
500-line/5,000-token SKILL.md ceiling, currently unenforced. Fixes the 28
resulting violations across 20 existing SKILL.md/agent files so the
enforcing pre-commit hook lands clean.

governance.md/CONTROLS.md were evaluated and excluded as rule sources -
they're org/CI-infrastructure controls, not prose patterns Vale can express.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QUDczvw1H3eEeMD29Q9Lbi

tests/test-skill-size-check.sh

@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+# Regression test for scripts/skill-size-check.sh: enforces agentskills.io's
+# 500-line/5,000-word(proxy-for-token) SKILL.md size ceiling.
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+SCRIPT="$REPO_ROOT/scripts/skill-size-check.sh"
+PASS=0
+FAIL=0
+
+pass() { echo "  PASS: $1"; PASS=$((PASS + 1)); }
+fail() { echo "  FAIL: $1"; FAIL=$((FAIL + 1)); }
+
+TMPDIR="$(mktemp -d)"
+trap 'rm -rf "$TMPDIR"' EXIT
+
+make_fixture() {
+  local name="$1" lines="$2" words_per_line="$3" file
+  file="$TMPDIR/$name.md"
+  {
+    echo "---"
+    echo "name: $name"
+    echo "description: Test fixture."
+    echo "---"
+    for ((i = 1; i <= lines; i++)); do
+      w=""
+      for ((j = 1; j <= words_per_line; j++)); do
+        w="$w word"
+      done
+      echo "$w"
+    done
+  } > "$file"
+  echo "$file"
+}
+
+echo ""
+echo "--- passes a file under both limits ---"
+SMALL="$(make_fixture small 10 5)"
+if "$SCRIPT" "$SMALL"; then
+  pass "file under both limits exits 0"
+else
+  fail "file under both limits should have exited 0"
+fi
+
+echo ""
+echo "--- fails a file over the line limit ---"
+MANY_LINES="$(make_fixture many-lines 600 1)"
+if "$SCRIPT" "$MANY_LINES" 2>/dev/null; then
+  fail "file over the 500-line ceiling should have exited non-zero"
+else
+  pass "file over the 500-line ceiling exits non-zero"
+fi
+
+echo ""
+echo "--- fails a file over the word-count limit ---"
+MANY_WORDS="$(make_fixture many-words 10 600)"
+if "$SCRIPT" "$MANY_WORDS" 2>/dev/null; then
+  fail "file over the 5,000-word ceiling should have exited non-zero"
+else
+  pass "file over the 5,000-word ceiling exits non-zero"
+fi
+
+echo ""
+echo "Results: $PASS passed, $FAIL failed"
+[[ $FAIL -eq 0 ]]