chore: remove .DS_Store and __pycache__ files, update .gitignore

Removes accidentally committed macOS and Python cache files from benchmark/.
Adds .DS_Store, __pycache__/*.pyc, cover*.out, and *.graph.{go,py} to .gitignore.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: greynewell

.gitignore

@@ -4,3 +4,18 @@ npm/bin/
 /supermodel
 /cli
 .supermodel/
+
+# macOS
+.DS_Store
+
+# Python
+__pycache__/
+*.pyc
+*.pyo
+
+# Go test coverage
+cover*.out
+
+# Supermodel graph sidecars
+*.graph.go
+*.graph.py