Splits the OAuth connect flow off entirely from signup/login so each
route has a single responsibility.
- routes/auth.php returns to its original state — redirect + callback
both back inside the `guest` group.
- routes/app.php gains a paired callback route at
/settings/authentication/providers/{provider}/callback.
- AuthenticationController::connectProvider /
connectProviderCallback override Socialite's redirectUrl so the
round-trip stays on the connect-flow URL. The Auth::check() branch
in the auth controllers is gone.
The OAuth apps in Google Cloud and GitHub Developer Settings need the
new callback URL registered alongside the existing one — documented in
.env.example.
79f800f858