claudetool: add "related files" detection to codereview tool

diff --git a/claudetool/testdata/passing_to_failing_subdir.txtar b/claudetool/testdata/passing_to_failing_subdir.txtar
index 7649554..1211912 100644
--- a/claudetool/testdata/passing_to_failing_subdir.txtar
+++ b/claudetool/testdata/passing_to_failing_subdir.txtar
@@ -24,6 +24,8 @@
 Break test
 
 -- .run_test --
+# Errors
+
 Test regressions detected between initial commit (8c6c71d0beac5e27b87dfc3f2fd9d274b62c3d3a) and HEAD:
 
 1: sketch.dev/foo.TestP: Was passing, now failing