chore: ignore .private/ folder for personal artefacts

Used to host user-only documents (e.g. internal meta-prompts,
methodology notes) that should never be pushed to the public repo.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: mac

.gitignore

@@ -50,3 +50,6 @@ docs/_autosummary/
 
 # Jupyter
 .ipynb_checkpoints/
+
+# personal / non-public artefacts
+.private/