OAuth login, improve default sign-up/in #2

OAuth login support is possible!!! But would it work with accounts of both regular and oauth types simultaneously? Should this also be based on a subdomain running on a server for year-long sessions, instead of the usual week-long ones?

Witchsky also needs automatic PDS resolution/detection based on the entered DID/handle, with fallback/email addresses to use witchsky.social. Other implementations are in https://deer.aylac.top/ and https://catsky.social/