refactor(application): co-locate each command/query with its handler

One file per use case under the feature folder (Tracks/PlayLists/Users),
dropping the Commands/Queries/Handlers sub-folders and their namespaces.
Each file now holds the record and its handler in namespace
Musify.Application.<Feature>; external usings updated accordingly.

Build: 0 warnings, 0 errors.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/Musify.Application/Tracks/Commands/CreateTrackCommand.cs

@@ -1,13 +0,0 @@
-using ErrorOr;
-using Mediator;
-using Musify.Application.Tracks.Responses;
-
-namespace Musify.Application.Tracks.Commands
-{
-    public record CreateTrackCommand(
-        long UserId,
-        string Title,
-        Guid PictureIntentId,
-        Guid AudioIntentId)
-        : ICommand<ErrorOr<TrackApplicationResponse>>;
-}

backend/Musify.Application/Tracks/Commands/DeleteTrackCommand.cs

@@ -1,10 +0,0 @@
-using ErrorOr;
-using Mediator;
-
-namespace Musify.Application.Tracks.Commands
-{
-    public record DeleteTrackCommand(
-        long UserId,
-        Guid TrackId)
-        : ICommand<ErrorOr<Success>>;
-}

backend/Musify.Application/Tracks/Commands/RequestTrackUploadUrlsCommand.cs

@@ -1,16 +0,0 @@
-using ErrorOr;
-using Mediator;
-using Musify.Application.Tracks.Responses;
-
-namespace Musify.Application.Tracks.Commands
-{
-    public record RequestTrackUploadUrlsCommand(
-        long UserId,
-        string PictureFileType,
-        string PictureContentType,
-        string AudioFileType,
-        string AudioContentType,
-        long? ExpectedPictureSizeBytes = null,
-        long? ExpectedAudioSizeBytes = null)
-        : ICommand<ErrorOr<TrackUploadUrlsResponse>>;
-}

backend/Musify.Application/Tracks/CreateTrack.cs

@@ -5,15 +5,21 @@ using Microsoft.Extensions.Logging;
 using Musify.Application.Configuration;
 using Musify.Application.Shared;
 using Musify.Application.Events;
-using Musify.Application.Tracks.Commands;
 using Musify.Application.Tracks.Responses;
 using Musify.Application.Services;
 using Musify.Domain.Entities;
 using Musify.Domain.ValueObjects;
 using Musify.Application.Contracts;
 
-namespace Musify.Application.Tracks.Handlers
+namespace Musify.Application.Tracks
 {
+    public record CreateTrackCommand(
+        long UserId,
+        string Title,
+        Guid PictureIntentId,
+        Guid AudioIntentId)
+        : ICommand<ErrorOr<TrackApplicationResponse>>;
+
     public class CreateTrackCommandHandler(
         IDatabase database,
         IEventBus eventBus,

backend/Musify.Application/Tracks/DeleteTrack.cs

@@ -2,13 +2,17 @@ using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
-using Musify.Application.Tracks.Commands;
 using Musify.Domain.ValueObjects;
 using Musify.Application.Events;
 using Musify.Application.Contracts;
 
-namespace Musify.Application.Tracks.Handlers
+namespace Musify.Application.Tracks
 {
+    public record DeleteTrackCommand(
+        long UserId,
+        Guid TrackId)
+        : ICommand<ErrorOr<Success>>;
+
     public class DeleteTrackCommandHandler(
         IDatabase database,
         IEventBus eventBus,
@@ -67,4 +71,4 @@ namespace Musify.Application.Tracks.Handlers
             return new Success();
         }
     }
-}
+}

backend/Musify.Application/Tracks/GetTrackById.cs

@@ -2,11 +2,13 @@ using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Musify.Application.Contracts;
-using Musify.Application.Tracks.Queries;
 using Musify.Application.Tracks.Responses;
 
-namespace Musify.Application.Tracks.Handlers
+namespace Musify.Application.Tracks
 {
+    public record GetTrackByIdQuery(Guid TrackId)
+        : IQuery<ErrorOr<TrackApplicationResponse>>;
+
     public class GetTrackByIdQueryHandler(IDatabase database)
         : IQueryHandler<GetTrackByIdQuery, ErrorOr<TrackApplicationResponse> >
     {
@@ -23,4 +25,4 @@ namespace Musify.Application.Tracks.Handlers
             return track;
         }
     }
-}
+}

backend/Musify.Application/Tracks/GetTrackStream.cs

@@ -4,12 +4,14 @@ using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
 using Musify.Application.Configuration;
 using Musify.Application.Contracts;
-using Musify.Application.Tracks.Queries;
 using Musify.Application.Tracks.Responses;
 using Musify.Domain.ValueObjects;
 
-namespace Musify.Application.Tracks.Handlers
+namespace Musify.Application.Tracks
 {
+    public record GetTrackStreamQuery(Guid TrackId, long UserId)
+        : IQuery<ErrorOr<TrackStreamResponse>>;
+
     public class GetTrackStreamQueryHandler(
         IDatabase database,
         IStreamTicketService ticketService,

backend/Musify.Application/Tracks/GetTracks.cs

@@ -2,13 +2,15 @@ using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Musify.Application.Pagination;
-using Musify.Application.Tracks.Queries;
 using Musify.Application.Tracks.Responses;
 using X.PagedList.EF;
 using Musify.Application.Contracts;
 
-namespace Musify.Application.Tracks.Handlers
+namespace Musify.Application.Tracks
 {
+    public record GetTracksQuery(int PageNumber = 1, int PageSize = 10)
+        : IQuery<ErrorOr<PaginatedResponse<TrackApplicationResponse> >>;
+
     public class GetTracksQueryHandler(IDatabase database)
         : IQueryHandler<GetTracksQuery, ErrorOr<PaginatedResponse<TrackApplicationResponse>> >
     {
@@ -26,4 +28,4 @@ namespace Musify.Application.Tracks.Handlers
             return PaginatedResponse<TrackApplicationResponse>.FromPagedList(pagedTracks);
         }
     }
-}
+}

backend/Musify.Application/Tracks/GetTracksByUserId.cs

@@ -2,13 +2,19 @@ using ErrorOr;
 using Mediator;
 using Microsoft.EntityFrameworkCore;
 using Musify.Application.Pagination;
-using Musify.Application.Tracks.Queries;
 using Musify.Application.Tracks.Responses;
 using X.PagedList.EF;
 using Musify.Application.Contracts;
 
-namespace Musify.Application.Tracks.Handlers
+namespace Musify.Application.Tracks
 {
+    public record GetTracksByUserIdQuery(
+        long UserId,
+    string? Name = null,
+        int PageNumber = 1,
+        int PageSize = 10)
+        : IQuery<ErrorOr<PaginatedResponse<TrackApplicationResponse> > >;
+
     public class GetTracksByUserIdQueryHandler(IDatabase database)
         : IQueryHandler<GetTracksByUserIdQuery, ErrorOr<PaginatedResponse<TrackApplicationResponse>> >
     {
@@ -38,4 +44,4 @@ namespace Musify.Application.Tracks.Handlers
             return PaginatedResponse<TrackApplicationResponse>.FromPagedList(pagedTracks);
         }
     }
-}
+}

backend/Musify.Application/Tracks/Queries/GetTrackByIdQuery.cs

@@ -1,9 +0,0 @@
-using ErrorOr;
-using Mediator;
-using Musify.Application.Tracks.Responses;
-
-namespace Musify.Application.Tracks.Queries
-{
-    public record GetTrackByIdQuery(Guid TrackId)
-        : IQuery<ErrorOr<TrackApplicationResponse>>;
-}

backend/Musify.Application/Tracks/Queries/GetTrackStreamQuery.cs

@@ -1,9 +0,0 @@
-using ErrorOr;
-using Mediator;
-using Musify.Application.Tracks.Responses;
-
-namespace Musify.Application.Tracks.Queries
-{
-    public record GetTrackStreamQuery(Guid TrackId, long UserId)
-        : IQuery<ErrorOr<TrackStreamResponse>>;
-}

backend/Musify.Application/Tracks/Queries/GetTracksByUserIdQuery.cs

@@ -1,14 +0,0 @@
-using ErrorOr;
-using Mediator;
-using Musify.Application.Pagination;
-using Musify.Application.Tracks.Responses;
-
-namespace Musify.Application.Tracks.Queries
-{
-    public record GetTracksByUserIdQuery(
-        long UserId,
-    string? Name = null,
-        int PageNumber = 1,
-        int PageSize = 10)
-        : IQuery<ErrorOr<PaginatedResponse<TrackApplicationResponse> > >;
-}

backend/Musify.Application/Tracks/Queries/GetTracksQuery.cs

@@ -1,10 +0,0 @@
-using ErrorOr;
-using Mediator;
-using Musify.Application.Pagination;
-using Musify.Application.Tracks.Responses;
-
-namespace Musify.Application.Tracks.Queries
-{
-    public record GetTracksQuery(int PageNumber = 1, int PageSize = 10)
-        : IQuery<ErrorOr<PaginatedResponse<TrackApplicationResponse> >>;
-}

backend/Musify.Application/Tracks/RequestTrackUploadUrls.cs

@@ -4,14 +4,23 @@ using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Logging;
 using Musify.Application.Configuration;
 using Musify.Application.Services;
-using Musify.Application.Tracks.Commands;
 using Musify.Application.Tracks.Responses;
 using Musify.Domain.Entities;
 using Musify.Domain.ValueObjects;
 using Musify.Application.Contracts;
 
-namespace Musify.Application.Tracks.Handlers
+namespace Musify.Application.Tracks
 {
+    public record RequestTrackUploadUrlsCommand(
+        long UserId,
+        string PictureFileType,
+        string PictureContentType,
+        string AudioFileType,
+        string AudioContentType,
+        long? ExpectedPictureSizeBytes = null,
+        long? ExpectedAudioSizeBytes = null)
+        : ICommand<ErrorOr<TrackUploadUrlsResponse>>;
+
     public class RequestTrackUploadUrlsCommandHandler(
         IDatabase database,
         UploadIntentValidator uploadIntentValidator,