claudetool: add "related files" detection to codereview tool

diff --git a/claudetool/testdata/passing_to_build_error.txtar b/claudetool/testdata/passing_to_build_error.txtar
index 9558862..6c7d1d0 100644
--- a/claudetool/testdata/passing_to_build_error.txtar
+++ b/claudetool/testdata/passing_to_build_error.txtar
@@ -24,6 +24,8 @@
 Break test with build error
 
 -- .run_test --
+# Errors
+
 Test regressions detected between initial commit (149798f10aaf06bc4700bb62d46ed6d8d88e35ad) and HEAD:
 
 1: sketch.dev: Was passing, now has build/vet errors