Remove YouTube integration from backend and deployment config

Drops the YouTube-backed second catalog source entirely: the
Local/External split on Track/Album collapses into single concrete
entities, Artist/TrackArtist/ExternalTrack/ExternalAlbum and the
YouTube service/download pipeline (yt-dlp, MassTransit consumer,
routing slip) are deleted, and mixes now source discovery only from
local listening history. Includes the RemoveYouTubeIntegration EF
Core migration and matching Worker/deploy/compose cleanup (no more
yt-dlp/python/deno in the Worker image, no thumbnail-cache/YtDlp
config sections).

backend/Hosts/Musify.Api/Endpoints/LikeEndpoints.cs

@@ -25,10 +25,8 @@ public static class LikeEndpoints
 
         group.MapPost("/toggle", ToggleTrackLike)
             .WithName("ToggleTrackLike")
-            .WithSummary("Like Or Unlike A Track, By Id Or By External Source, Provisioning It In The Background If Needed.")
-            .AddEndpointFilter<ValidationFilter<ToggleLikeRequest>>()
+            .WithSummary("Like Or Unlike A Track By Id.")
             .Produces<bool>()
-            .ProducesValidationProblem()
             .Produces(StatusCodes.Status401Unauthorized)
             .Produces(StatusCodes.Status404NotFound);
 
@@ -53,7 +51,7 @@ public static class LikeEndpoints
         CancellationToken cancellationToken)
     {
         var result = await mediator.Send(
-            new ToggleTrackLikeCommand(currentUser.RequiredId, request.TrackId, request.Source, request.ExternalId),
+            new ToggleTrackLikeCommand(currentUser.RequiredId, request.TrackId),
             cancellationToken);
 
         return result.ToHttpResult();