refactor: standardize project names to Musify.* and flatten layout

- Flatten nested per-repo folders into flat Musify.* projects at root
- Rename assemblies/csproj: Domain->Musify.Domain, Application->Musify.Application,
  Infrastructure->Musify.Infrastructure, WebApi->Musify.Api, Worker->Musify.Worker,
  StreamingGateway->Musify.StreamingGateway
- Rename WebApi.* namespaces to Musify.Api.*
- Update all ProjectReference paths and the solution file
- Consolidate stray per-repo dotfiles; add root .gitattributes
- Move flutter client out to _archive

Musify.Application/Extensions/ResultExtensions.cs

@@ -0,0 +1,25 @@
+using Ardalis.Result;
+
+namespace Musify.Application.Extensions;
+
+public static class ResultExtensions
+{
+    public static Result<TOut> As<TIn, TOut>(this Result<TIn> result)
+    {
+        return result.Status switch
+        {
+            ResultStatus.Ok or
+            ResultStatus.Created or
+            ResultStatus.NoContent   => throw new InvalidOperationException($"Cannot convert a successful result ( {result.Status} ) to another type. Use Map or Bind instead."),
+            ResultStatus.NotFound    => Result<TOut>.NotFound(result.Errors.ToArray()),
+            ResultStatus.Forbidden   => Result<TOut>.Forbidden(result.Errors.ToArray()),
+            ResultStatus.Unauthorized => Result<TOut>.Unauthorized(result.Errors.ToArray()),
+            ResultStatus.Invalid     => Result<TOut>.Invalid(result.ValidationErrors.ToArray()),
+            ResultStatus.Conflict    => Result<TOut>.Conflict(result.Errors.ToArray()),
+            ResultStatus.CriticalError => Result<TOut>.CriticalError(result.Errors.ToArray()),
+            ResultStatus.Unavailable => Result<TOut>.Unavailable(result.Errors.ToArray()),
+            ResultStatus.Error       => Result<TOut>.Error(string.Join(";", result.Errors)),
+            _                        => Result<TOut>.Error(string.Join(";", result.Errors))
+        };
+    }
+}