claudetool: add "related files" detection to codereview tool

diff --git a/claudetool/testdata/mark_test_skipped.txtar b/claudetool/testdata/mark_test_skipped.txtar
index bf887e3..d834ae4 100644
--- a/claudetool/testdata/mark_test_skipped.txtar
+++ b/claudetool/testdata/mark_test_skipped.txtar
@@ -24,6 +24,8 @@
 Skip test
 
 -- .run_test --
+# Errors
+
 Test regressions detected between initial commit (851ba0628e0e2d93e27e168d6af336f3e4d375c7) and HEAD:
 
 1: sketch.dev.TestP: Was passing, now skipped