Disable automatic Git checkpoints.

Sessions create Git checkpoints automatically. Not the AI, the app itself. This is highly undesirable because the system won't clean them up and git UI commonly doesn't allow erasing them either. Couldn't find a setting to disable them.

No files or tests are named. Start by locating where the app creates automatic Git checkpoints and where session settings are defined; done means users can disable checkpoint creation and the behavior is covered by an appropriate test.

Written by the indexing model from the issue text.