LOCK setting for UPDATE AUTH transactions

I think it would be a good security feature to have a LOCK setting (locked by default) which would need to be explicitly unlocked in order to have the ability to sign any UPDATE AUTH transactions.

While locked, if the user attempts to initiate an UPDATE AUTH action, they would get a message saying that action is locked and must be explicitly unlocked in settings before attempting again.

When unlocked, there should be a double confirmation along with highly visible warning something along the lines of "This is a dangerous action which could result in losing control of your account, etc etc".

After unlocking, it should automatically lock again after some period of time.

No files, tests, or entry points are named. Review the existing UPDATE AUTH signing flow and settings behavior first, then define the locked default, explicit unlock flow, double confirmation, warning, and automatic relock timeout; done means each requested safeguard is implemented and the locked attempt shows the specified message.

Written by the indexing model from the issue text.