.gitignore: exclude __pycache__ (codereg dialogs are Python 3 now)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ScTj9M9ctPk9ySXcDdt9j9

Author: andy

.gitignore

@@ -5,6 +5,7 @@
 /obj/
 /build-cmake/
 src/apps/symmetry/*.mod
+__pycache__/
 
 # Claude Code local session/settings state, not repo content
 /.claude/