Clean up Application layer commands/queries readability and correctness

Add missing AsNoTracking() on read-only queries, drop redundant
Update() calls on already-tracked entities, and fix inconsistent
formatting (stray spaces in generics, ternaries, and lambdas) across
the Albums/Tracks/PlayLists/Users command and query handlers.

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

@@ -28,7 +28,7 @@ namespace Musify.Application.Users
     }
 
     public class CreateUserCommandHandler(IDatabase database, ILogger<CreateUserCommandHandler> logger)
-        : ICommandHandler<CreateUserCommand, ErrorOr<UserApplicationResponse> >
+        : ICommandHandler<CreateUserCommand, ErrorOr<UserApplicationResponse>>
     {
         public async ValueTask<ErrorOr<UserApplicationResponse>> Handle(CreateUserCommand request, CancellationToken cancellationToken)
         {

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

@@ -16,6 +16,7 @@ namespace Musify.Application.Users
             var weekAgo = DateTime.UtcNow.AddDays(-7);
 
             var thisWeekHistory = database.ListeningHistories
+                .AsNoTracking()
                 .Where(l => l.UserId == request.UserId && l.ListenedAt >= weekAgo);
 
             var tracksThisWeek = await thisWeekHistory
@@ -24,10 +25,11 @@ namespace Musify.Application.Users
                 .CountAsync(cancellationToken);
 
             var secondsThisWeek = await thisWeekHistory
-                .Join(database.Tracks, l => l.TrackId, t => t.Id, (l, t) => t.DurationSeconds)
+                .Join(database.Tracks.AsNoTracking(), l => l.TrackId, t => t.Id, (l, t) => t.DurationSeconds)
                 .SumAsync(cancellationToken);
 
             var listenedDates = await database.ListeningHistories
+                .AsNoTracking()
                 .Where(l => l.UserId == request.UserId)
                 .Select(l => l.ListenedAt.Date)
                 .Distinct()

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

@@ -7,10 +7,10 @@ using Musify.Application.Users.Responses;
 namespace Musify.Application.Users
 {
     public record GetUserByIdQuery(long Id)
-        : IQuery<ErrorOr<UserApplicationResponse> >;
+        : IQuery<ErrorOr<UserApplicationResponse>>;
 
     public class GetUserByIdQueryHandler(IDatabase database)
-        : IQueryHandler<GetUserByIdQuery, ErrorOr<UserApplicationResponse> >
+        : IQueryHandler<GetUserByIdQuery, ErrorOr<UserApplicationResponse>>
     {
         public async ValueTask<ErrorOr<UserApplicationResponse>> Handle(GetUserByIdQuery request, CancellationToken cancellationToken)
         {

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

@@ -9,29 +9,29 @@ using Musify.Application.Contracts;
 namespace Musify.Application.Users
 {
     public record GetUsersQuery(int PageNumber, int PageSize, string? UsernameSearch)
-        : IQuery<ErrorOr<PaginatedResponse<UserApplicationResponse> >>;
+        : IQuery<ErrorOr<PaginatedResponse<UserApplicationResponse>>>;
 
     public class GetUsersQueryHandler(IDatabase database)
-        : IQueryHandler<GetUsersQuery, ErrorOr<PaginatedResponse<UserApplicationResponse> > >
+        : IQueryHandler<GetUsersQuery, ErrorOr<PaginatedResponse<UserApplicationResponse>>>
     {
-        public async ValueTask<ErrorOr<PaginatedResponse<UserApplicationResponse> >> Handle(GetUsersQuery request, CancellationToken cancellationToken)
+        public async ValueTask<ErrorOr<PaginatedResponse<UserApplicationResponse>>> Handle(GetUsersQuery request, CancellationToken cancellationToken)
         {
-            var user = database.Users
+            var usersQuery = database.Users
                 .AsNoTracking()
                 .AsQueryable();
 
             if (!string.IsNullOrEmpty(request.UsernameSearch))
             {
                 var normalizedUsername = request.UsernameSearch.Trim().ToUpperInvariant();
-                user = user.Where(u => u.NormalizedName.Contains(normalizedUsername));
+                usersQuery = usersQuery.Where(u => u.NormalizedName.Contains(normalizedUsername));
             }
 
-            var totalCount = await user.CountAsync(cancellationToken);
-            var pagedUser = await user
+            var totalCount = await usersQuery.CountAsync(cancellationToken);
+            var pagedUsers = await usersQuery
                 .Select(u => UserApplicationResponse.FromEntity(u))
                 .ToPagedListAsync(request.PageNumber, request.PageSize, totalCount, cancellationToken);
 
-            return PaginatedResponse<UserApplicationResponse>.FromPagedList(pagedUser);
+            return PaginatedResponse<UserApplicationResponse>.FromPagedList(pagedUsers);
         }
     }
 }