fix(lint): fail the style-sync check when one copy is missing

The guard used `||`, so exactly one of the two audit skill directories
missing also exited 0, where the intended silent no-op is both absent.
A renamed skill-audit reported green instead of flagging that a
canonical style copy had lost its counterpart.

One-present now exits 1 naming the missing side and the remedy.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MCQ648fLSFXPHGZdQ8gn58

tests/test-check-vale-style-sync.sh

@@ -86,6 +86,27 @@ else
   fail "exited non-zero when skill-audit/agent-audit are simply absent"
 fi
 
+# --- 6. Exits 1 when only one of the two copies is present ---
+# The no-op guard used `||`, so a single missing copy also exited 0 — a deleted
+# or renamed copy passed the sync check silently.
+echo ""
+echo "--- exits 1 when only one of the two copies is present ---"
+FIXTURE6="$(make_fixture)"
+FIXTURE7="$(make_fixture)"
+trap 'rm -rf "$FIXTURE" "$FIXTURE2" "$FIXTURE3" "$FIXTURE4" "$FIXTURE5" "$FIXTURE6" "$FIXTURE7"' EXIT
+rm -rf "$FIXTURE6/plugins/kyberforge/skills/skill-audit"
+rm -rf "$FIXTURE7/plugins/kyberforge/skills/agent-audit"
+if bash "$SCRIPT" "$FIXTURE6" > /dev/null 2>&1; then
+  fail "exited 0 when only agent-audit is present — expected exit 1"
+else
+  pass "exits non-zero when skill-audit's copy is missing but agent-audit's is present"
+fi
+if bash "$SCRIPT" "$FIXTURE7" > /dev/null 2>&1; then
+  fail "exited 0 when only skill-audit is present — expected exit 1"
+else
+  pass "exits non-zero when agent-audit's canonical copy is missing but skill-audit's is present"
+fi
+
 echo ""
 echo "Results: $PASS passed, $FAIL failed"
 [[ $FAIL -eq 0 ]]