refactor: replace Ardalis.Result with ErrorOr across the app

Ardalis Result<T> carried incoherent success sub-statuses and a clunky
generic converter; ErrorOr models success-or-errors cleanly.

- Application: all commands/queries/handlers now return ErrorOr<T>
  (non-generic Result -> ErrorOr<Success>); errors via Error.NotFound/
  Conflict/Validation/Unauthorized/Failure; success via value or new Success()
- Drop ResultExtensions.As<>(): error propagation is now just return .Errors
- Rewrite HTTP mapping (ErrorOrHttpExtensions) off Error.Type; success maps
  to 200 (value) or 204 (Success); Created still built in the endpoints
- Endpoints/gateway middleware: !IsSuccess -> IsError
- Swap Ardalis.Result package for ErrorOr 2.1.1 (remove unused ref from Worker)

Build: 0 warnings, 0 errors.

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

backend/Musify.Api/Endpoints/PlayListEndpoints.cs

@@ -119,7 +119,7 @@ public static class PlayListEndpoints
             new CreatePlayListCommand(currentUser.RequiredId, request.Name, request.Description, request.PictureIntentId),
             cancellationToken);
 
-        if (!result.IsSuccess)
+        if (result.IsError)
             return result.ToHttpResult();
 
         return Results.Created($"/playlists/{result.Value.Id}", result.Value);

backend/Musify.Api/Endpoints/TrackEndpoints.cs

@@ -103,7 +103,7 @@ public static class TrackEndpoints
             new CreateTrackCommand(currentUser.RequiredId, request.Title, request.PictureIntentId, request.AudioIntentId),
             cancellationToken);
 
-        if (!result.IsSuccess)
+        if (result.IsError)
             return result.ToHttpResult();
 
         return Results.Created($"/tracks/{result.Value.Id}", result.Value);

backend/Musify.Api/Endpoints/UserEndpoints.cs

@@ -59,7 +59,7 @@ public static class UserEndpoints
             new CreateUserCommand(request.Id, request.Name, request.FirstName, request.SecondName),
             cancellationToken);
 
-        if (!result.IsSuccess)
+        if (result.IsError)
             return result.ToHttpResult();
 
         return Results.Created($"/users/{result.Value.Id}", result.Value);

backend/Musify.Api/Extensions/ErrorOrHttpExtensions.cs

@@ -0,0 +1,38 @@
+using ErrorOr;
+using IResult = Microsoft.AspNetCore.Http.IResult;
+
+namespace Musify.Api.Extensions;
+
+public static class ErrorOrHttpExtensions
+{
+    public static IResult ToHttpResult<T>(this ErrorOr<T> result)
+    {
+        if (result.IsError)
+            return Problem(result.Errors);
+
+        return result.Value is Success
+            ? Results.NoContent()
+            : Results.Ok(result.Value);
+    }
+
+    private static IResult Problem(List<Error> errors)
+    {
+        if (errors.All(e => e.Type == ErrorType.Validation))
+            return Results.ValidationProblem(ToValidationDictionary(errors));
+
+        var error = errors[0];
+        return error.Type switch
+        {
+            ErrorType.NotFound => Results.NotFound(error.Description),
+            ErrorType.Unauthorized => Results.Unauthorized(),
+            ErrorType.Forbidden => Results.StatusCode(StatusCodes.Status403Forbidden),
+            ErrorType.Conflict => Results.Conflict(error.Description),
+            _ => Results.Problem(error.Description)
+        };
+    }
+
+    private static Dictionary<string, string[]> ToValidationDictionary(IEnumerable<Error> errors) =>
+        errors
+            .GroupBy(e => string.IsNullOrEmpty(e.Code) ? "general" : e.Code)
+            .ToDictionary(g => g.Key, g => g.Select(e => e.Description).ToArray());
+}

backend/Musify.Api/Extensions/ResultHttpExtensions.cs

@@ -1,36 +0,0 @@
-using Ardalis.Result;
-using IResult = Microsoft.AspNetCore.Http.IResult;
-
-namespace Musify.Api.Extensions;
-
-public static class ResultHttpExtensions
-{
-    public static IResult ToHttpResult(this Result result) =>
-        result.Status switch
-        {
-            ResultStatus.Ok or ResultStatus.NoContent => Results.NoContent(),
-            ResultStatus.NotFound => Results.NotFound(result.Errors.FirstOrDefault()),
-            ResultStatus.Invalid => Results.ValidationProblem(ToValidationDictionary(result.ValidationErrors)),
-            ResultStatus.Unauthorized => Results.Unauthorized(),
-            ResultStatus.Forbidden => Results.StatusCode(StatusCodes.Status403Forbidden),
-            ResultStatus.Conflict => Results.Conflict(result.Errors.FirstOrDefault()),
-            _ => Results.Problem(string.Join(", ", result.Errors))
-        };
-
-    public static IResult ToHttpResult<T>(this Result<T> result) =>
-        result.Status switch
-        {
-            ResultStatus.Ok => Results.Ok(result.Value),
-            ResultStatus.NotFound => Results.NotFound(result.Errors.FirstOrDefault()),
-            ResultStatus.Invalid => Results.ValidationProblem(ToValidationDictionary(result.ValidationErrors)),
-            ResultStatus.Unauthorized => Results.Unauthorized(),
-            ResultStatus.Forbidden => Results.StatusCode(StatusCodes.Status403Forbidden),
-            ResultStatus.Conflict => Results.Conflict(result.Errors.FirstOrDefault()),
-            _ => Results.Problem(string.Join(", ", result.Errors))
-        };
-
-    private static Dictionary<string, string[]> ToValidationDictionary(IEnumerable<ValidationError> errors) =>
-        errors
-            .GroupBy(e => string.IsNullOrEmpty(e.Identifier) ? "general" : e.Identifier)
-            .ToDictionary(g => g.Key, g => g.Select(e => e.ErrorMessage).ToArray());
-}

backend/Musify.Api/Musify.Api.csproj

@@ -5,7 +5,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Ardalis.Result" />
+    <PackageReference Include="ErrorOr" />
     <PackageReference Include="AWSSDK.S3" />
     <PackageReference Include="FluentValidation.DependencyInjectionExtensions" />
     <PackageReference Include="MassTransit" />