Alter admin/mod keys if admins/mods are removed

This covers a case like the following:

1. User joins a cabal with a url like `cabal://abcdef?adminKey=deafcb`
2. User runs `/unadmin deafcb`
3. User quits cabal and re-launches
4. `deafcb` is once again an admin

There's also a case where Step 3 is instead "User shares the cabal uri on the top right corner and makes `deafcb` admin on others without intending it)".

I think the fix would be to move admin and mod keys to cabal-cli, and have the url we show on the top right update to reflect current admin/mod keys.

Start by tracing the /unadmin command, cabal lifecycle across quitting and relaunching, and construction of the cabal URI shown in the top-right corner. Confirm where admin and mod keys are retained, then verify that removing an admin or mod persists and that the displayed URI reflects the current keys.

Written by the indexing model from the issue text.