chore: ignore local notebooks/ exploratory tree

Keep notebooks untracked so public Research does not grow notebook noise.

Author: Claude Code (Delicious233)

.gitignore

@@ -225,6 +225,8 @@ coverage.xml
 
 # Jupyter
 .ipynb_checkpoints/
+# Local exploratory notebooks (keep untracked; public Research must not grow notebook noise)
+notebooks/
 
 # Environment files
 .env