chore: ignore handoffs/ + working/ per portfolio baseline

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: snapsynapse

.gitignore

@@ -42,3 +42,7 @@ dist/
 build/
 .venv/
 venv/
+
+# --- portfolio baseline (2026-07-04): transient dirs ---
+handoffs/
+working/