audit/provide alternative option to nanoid for account ids

In a large system, using nanoid for account id's might cause a serious bug (people being able to edit accounts that aren't theirs). It would be good for people to provide their own id's, or at least think more about this issue.

Start by auditing how nanoid-generated account IDs are created and used for account lookup; the payload names no files or tests, so trace those entry points before deciding scope. Done means the security risk is assessed and a concrete direction is recorded for whether user-provided IDs or an alternative to nanoid is needed.

Written by the indexing model from the issue text.