Clean up memory when it becomes stale, broad, duplicated, or misleading.

## Cleanup routine

Safe cleanup process:

1. Back up memory first.
2. Open the memory and read the current content.
3. Decide whether to update, split, move, deprecate, or delete.
4. Keep useful history when a fact changed but still explains past decisions.
5. Run recall queries after cleanup to confirm the right nodes appear.

Prefer splitting broad memories over deleting them immediately. A broad memory often contains one or two useful facts mixed with stale detail.
