claudetool: add "related files" detection to codereview tool

diff --git a/claudetool/testdata/skipped_to_build_error.txtar b/claudetool/testdata/skipped_to_build_error.txtar
index f648572..671b53b 100644
--- a/claudetool/testdata/skipped_to_build_error.txtar
+++ b/claudetool/testdata/skipped_to_build_error.txtar
@@ -25,6 +25,8 @@
 Change skipped test to test with build error
 
 -- .run_test --
+# Errors
+
 Test regressions detected between initial commit (3635353dfefb2fa652728318567209ccfc4aba42) and HEAD:
 
 1: sketch.dev: Was passing, now has build/vet errors