Make all users admins: update schema default, add migration, simplify registration and OAuth flows

Co-authored-by: xCyanGrizzly <53275238+xCyanGrizzly@users.noreply.github.com>

prisma/schema.prisma

@@ -22,7 +22,7 @@ model User {
   emailVerified  DateTime?
   image          String?
   hashedPassword String?
-  role           Role      @default(USER)
+  role           Role      @default(ADMIN)
   createdAt      DateTime  @default(now())
   updatedAt      DateTime  @updatedAt