Fix Task 5 review issues: per-test ApiFactory, drop dead RoleManager param + EF Core using

backend/Auth/AuthEndpoints.cs

@@ -1,6 +1,5 @@
 using Microsoft.AspNetCore.Identity;
 using Microsoft.AspNetCore.Mvc;
-using Microsoft.EntityFrameworkCore;
 
 namespace backend.Auth;
 
@@ -15,8 +14,7 @@ public static class AuthEndpoints
 
         grp.MapPost("/register", async (
             [FromBody] RegisterRequest req,
-            UserManager<ApplicationUser> users,
-            RoleManager<IdentityRole<Guid>> roles) =>
+            UserManager<ApplicationUser> users) =>
         {
             var user = new ApplicationUser { UserName = req.Email, Email = req.Email };
             var create = await users.CreateAsync(user, req.Password);