Reorganize backend to mirror Musify.slnx folder structure

Moves the six backend projects on disk into Core/ and Hosts/
subfolders, matching the solution folders already defined in
Musify.slnx, so the file explorer reflects the same layout as the
solution:

  backend/Core/Musify.Domain
  backend/Core/Musify.Application
  backend/Core/Musify.Infrastructure
  backend/Hosts/Musify.Api
  backend/Hosts/Musify.Worker
  backend/Hosts/Musify.StreamingGateway

Updates every reference to the old paths: ProjectReference entries in
Musify.Api.csproj and Musify.Worker.csproj, the three Dockerfiles,
deploy/scripts/migrate.ps1|sh, deploy/zitadel/provision.ps1,
deploy/up.ps1, deploy/README.md and docs/development.md. Also fixes a
stale Dockerfile comment pointing at a compose file that no longer
exists.

Verified with `dotnet build Musify.slnx` against the new layout.

backend/Core/Musify.Application/Events/CreatePlayListResourcesEvent.cs

@@ -0,0 +1,14 @@
+using Musify.Application.Shared;
+
+namespace Musify.Application.Events
+{
+    public record CreatePlayListResourcesEvent(
+        Guid PlayListId,
+        Guid PictureIntentId,
+        string Bucket,
+        string PictureSourceKey,
+        string PictureDestinationKey,
+        ImageSize Small,
+        ImageSize Medium,
+        ImageSize Large);
+}

backend/Core/Musify.Application/Events/CreateTrackResourcesEvent.cs

@@ -0,0 +1,18 @@
+using Musify.Application.Shared;
+
+namespace Musify.Application.Events
+{
+    public record CreateTrackResourcesEvent(
+        Guid TrackId,
+        Guid PictureIntentId,
+        Guid AudioIntentId,
+        string Bucket,
+        string PictureSourceKey,
+        string PictureDestinationKey,
+        string AudioSourceKey,
+        string AudioDestinationKey,
+        string AudioProcessedFolderKey,
+        ImageSize Small,
+        ImageSize Medium,
+        ImageSize Large);
+}

backend/Core/Musify.Application/Events/DeletePlayListEvent.cs

@@ -0,0 +1,6 @@
+namespace Musify.Application.Events
+{
+    public record DeletePlayListEvent(
+        Guid PlayListId,
+        long UserId);
+}

backend/Core/Musify.Application/Events/DeleteTrackEvent.cs

@@ -0,0 +1,6 @@
+namespace Musify.Application.Events
+{
+    public record DeleteTrackEvent(
+        Guid TrackId,
+        long UserId);
+}

backend/Core/Musify.Application/Events/DownloadYouTubeTrackEvent.cs

@@ -0,0 +1,14 @@
+using Musify.Application.Shared;
+
+namespace Musify.Application.Events
+{
+    public record DownloadYouTubeTrackEvent(
+        Guid TrackId,
+        string VideoId,
+        string ThumbnailUrl,
+        string Bucket,
+        string AudioProcessedFolderKey,
+        ImageSize Small,
+        ImageSize Medium,
+        ImageSize Large);
+}

backend/Core/Musify.Application/Events/PlayListPictureProcessed.cs

@@ -0,0 +1,4 @@
+namespace Musify.Application.Events
+{
+    public record PlayListPictureProcessed(Guid PlayListId);
+}

backend/Core/Musify.Application/Events/PlayListPictureProcessingFailed.cs

@@ -0,0 +1,4 @@
+namespace Musify.Application.Events
+{
+    public record PlayListPictureProcessingFailed(Guid PlayListId);
+}

backend/Core/Musify.Application/Events/PlayListProcessingFailed.cs

@@ -0,0 +1,7 @@
+namespace Musify.Application.Events
+{
+    public record PlayListProcessingFailed(
+        Guid PlayListId,
+        string? Bucket,
+        string? PictureKey);
+}

backend/Core/Musify.Application/Events/TrackAudioProcessed.cs

@@ -0,0 +1,4 @@
+namespace Musify.Application.Events
+{
+    public record TrackAudioProcessed(Guid TrackId);
+}

backend/Core/Musify.Application/Events/TrackAudioProcessingFailed.cs

@@ -0,0 +1,4 @@
+namespace Musify.Application.Events
+{
+    public record TrackAudioProcessingFailed(Guid TrackId);
+}

backend/Core/Musify.Application/Events/TrackPictureProcessed.cs

@@ -0,0 +1,4 @@
+namespace Musify.Application.Events
+{
+    public record TrackPictureProcessed(Guid TrackId);
+}

backend/Core/Musify.Application/Events/TrackPictureProcessingFailed.cs

@@ -0,0 +1,4 @@
+namespace Musify.Application.Events
+{
+    public record TrackPictureProcessingFailed(Guid TrackId);
+}

backend/Core/Musify.Application/Events/TrackProcessingFailed.cs

@@ -0,0 +1,8 @@
+namespace Musify.Application.Events
+{
+    public record TrackProcessingFailed(
+        Guid TrackId,
+        string? Bucket,
+        string? PictureKey,
+        string? AudioKey);
+}

backend/Core/Musify.Application/Events/UpdatePlayListPictureEvent.cs

@@ -0,0 +1,12 @@
+using Musify.Application.Shared;
+
+namespace Musify.Application.Events
+{
+    public record UpdatePlayListPictureEvent(
+        Guid PlayListId,
+        string Bucket,
+        string SourceKey,
+        ImageSize Small,
+        ImageSize Medium,
+        ImageSize Large);
+}

backend/Core/Musify.Application/Events/UpdatePlayListPictureSourceEvent.cs

@@ -0,0 +1,14 @@
+using Musify.Application.Shared;
+
+namespace Musify.Application.Events
+{
+    public record UpdatePlayListPictureSourceEvent(
+        Guid PlayListId,
+        Guid PictureIntentId,
+        string Bucket,
+        string PictureSourceKey,
+        string PictureDestinationKey,
+        ImageSize Small,
+        ImageSize Medium,
+        ImageSize Large);
+}

backend/Core/Musify.Application/Events/UpdateTrackAudioEvent.cs

@@ -0,0 +1,9 @@
+namespace Musify.Application.Events
+{
+    public record UpdateTrackAudioEvent(
+        Guid TrackId,
+        string SourceBucket,
+        string SourceKey,
+        string DestinationBucket,
+        string DestinationFolderKey);
+}

backend/Core/Musify.Application/Events/UpdateTrackPictureEvent.cs

@@ -0,0 +1,12 @@
+using Musify.Application.Shared;
+
+namespace Musify.Application.Events
+{
+    public record UpdateTrackPictureEvent(
+        Guid TrackId,
+        string Bucket,
+        string SourceKey,
+        ImageSize Small,
+        ImageSize Medium,
+        ImageSize Large);
+}