claudetool: add "related files" detection to codereview tool
diff --git a/claudetool/testdata/empty_testdir_add_file.txtar b/claudetool/testdata/empty_testdir_add_file.txtar
index b754f3d..7c2be2d 100644
--- a/claudetool/testdata/empty_testdir_add_file.txtar
+++ b/claudetool/testdata/empty_testdir_add_file.txtar
@@ -29,6 +29,8 @@
Add non-empty file to testdata
-- .run_test --
+# Errors
+
Test regressions detected between initial commit (cdc9ec6dfb8669c11d8aa0df49c72112627784dc) and HEAD:
1: sketch.dev.TestEmptyTestdata: Was passing, now failing