Let users browse followers and following lists

Following lists are public; followers are visible to the user and to mutual followers.
Adds GET /users/{id}/followers and /following, exposes isFollowing and canViewFollowers
on the profile, and returns isFollowedByViewer from user search so the web player no
longer calls /is-following per user.

backend/Core/Musify.Application/Users/GetUsers.cs

@@ -8,13 +8,13 @@ using Musify.Application.Contracts;
 
 namespace Musify.Application.Users
 {
-    public record GetUsersQuery(int PageNumber, int PageSize, string? UsernameSearch)
-        : IQuery<ErrorOr<PaginatedResponse<UserApplicationResponse>>>;
+    public record GetUsersQuery(int PageNumber, int PageSize, string? UsernameSearch, long? ViewerId = null)
+        : IQuery<ErrorOr<PaginatedResponse<UserSummaryResponse>>>;
 
     public class GetUsersQueryHandler(IDatabase database)
-        : IQueryHandler<GetUsersQuery, ErrorOr<PaginatedResponse<UserApplicationResponse>>>
+        : IQueryHandler<GetUsersQuery, ErrorOr<PaginatedResponse<UserSummaryResponse>>>
     {
-        public async ValueTask<ErrorOr<PaginatedResponse<UserApplicationResponse>>> Handle(GetUsersQuery request, CancellationToken cancellationToken)
+        public async ValueTask<ErrorOr<PaginatedResponse<UserSummaryResponse>>> Handle(GetUsersQuery request, CancellationToken cancellationToken)
         {
             var usersQuery = database.Users
                 .AsNoTracking()
@@ -27,11 +27,19 @@ namespace Musify.Application.Users
             }
 
             var totalCount = await usersQuery.CountAsync(cancellationToken);
+            var viewerId = request.ViewerId;
             var pagedUsers = await usersQuery
-                .Select(u => UserApplicationResponse.FromEntity(u))
+                .OrderBy(u => u.Name)
+                .Select(u => new UserSummaryResponse(
+                    u.Id,
+                    u.Name,
+                    u.FirstName,
+                    u.SecondName,
+                    u.ProfilePictureUrl,
+                    viewerId != null && database.UserFollows.Any(f => f.FollowerId == viewerId && f.FollowedId == u.Id)))
                 .ToPagedListAsync(request.PageNumber, request.PageSize, totalCount, cancellationToken);
 
-            return PaginatedResponse<UserApplicationResponse>.FromPagedList(pagedUsers);
+            return PaginatedResponse<UserSummaryResponse>.FromPagedList(pagedUsers);
         }
     }
 }