Check and fix missing profiles in the KV store

This runs through each profile ID in the `Profiles` table and checks whether
it's in the KV store. Yes, it loads all the profile IDs in one DB call - since
it's the primary key, that comes back real quick, and it's only a few MB. Didn't
feel worth spending the time on paging.

With the `--fix` option, the script will save to the KV store any profiles not
found in it yet. It does this simply by calling `allSet` with no updates (it's
really a merge, not a set). The get performed will fall back and load from the
`Profiles` table, and then the save happens on the KV store.