chore(gitignore): ignore harness diagnostic report bundles

reports/*.tar.gz bundles logs and session state; pushing them to Gitea would
publish raw transcript material.

.gitignore

@@ -60,6 +60,9 @@ puppeteer/
 # harness runtime transcripts: local-only, may contain raw session secrets
 agent/sessions/
 
+# harness diagnostic report bundles (tarballs of logs + session state)
+reports/
+
 # --- agent runtime scratch: research runs, decode predictions, worktrees ----
 autoresearch/
 agent/predict/