Update Memory

Replace the user's entire memory structure.

This is how users "delete" items - they remove them client-side and send the complete updated structure back.

Uses optimistic locking via version field:

• Request must include the version the user is updating from
• If version doesn't match current DB version, returns 409 Conflict
• This prevents silent overwrites when nightly cron runs concurrently
• User's actions are always source of truth - they just need to retry