claudetool/codereview: fix runGenerate to filter pre-existing modified files

The runGenerate function was returning all files that appear modified in git
status after running 'go generate', including files that were already modified
before the generate command ran. This led to misleading output suggesting that
'go generate' had changed files like .DS_Store, .projections.json, and other
unrelated dirty files.

Co-Authored-By: sketch <hello@sketch.dev>
Change-ID: sfdde2d72136bfb64k
diff --git a/claudetool/codereview/codereview.go b/claudetool/codereview/codereview.go
index 085479e..c729c30 100644
--- a/claudetool/codereview/codereview.go
+++ b/claudetool/codereview/codereview.go
@@ -391,7 +391,11 @@
 		if path == "" {
 			continue
 		}
-		changed = append(changed, filepath.Join(r.repoRoot, path))
+		absPath := filepath.Join(r.repoRoot, path)
+		if statusesContainFile(r.initialStatus, absPath) {
+			continue
+		}
+		changed = append(changed, absPath)
 	}
 
 	return changed, nil