Use User::PrimaryKeyType all over

There's a few spots that use Int64 and assumes that is the User's ID type, but we can use `User::PrimaryKeyType` instead which will resolve as Int64 or UUID... or really whatever you're using.

Search the repository for Int64 usages associated with User IDs and inspect the surrounding User::PrimaryKeyType references first. Update each relevant spot so generated applications work with Int64, UUID, or another configured primary-key type, then run the available test or generation checks.

Written by the indexing model from the issue text.