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.Infrastructure/MassTransit/Activities/PlayLists/DeletePlayListFromDbActivity.cs

@@ -0,0 +1,36 @@
+using MassTransit;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using Musify.Application.Contracts;
+using Musify.Infrastructure.MassTransit.Arguments;
+
+namespace Musify.Infrastructure.MassTransit.Activities.PlayLists
+{
+    internal class DeletePlayListFromDbActivity(
+        IDatabase database,
+        ILogger<DeletePlayListFromDbActivity> logger)
+        : IExecuteActivity<DeletePlayListFromDbArguments>
+    {
+        public const string ExecuteEndpointName = "delete-playList-from-db";
+
+        public async Task<ExecutionResult> Execute(ExecuteContext<DeletePlayListFromDbArguments> executeContext)
+        {
+            var playList = await database.PlayLists
+                .SingleOrDefaultAsync(p => p.Id == executeContext.Arguments.PlayListId, executeContext.CancellationToken);
+
+            if (playList is null)
+            {
+                logger.LogInformation(
+                    "PlayList {PlayListId} not found while deleting from DB, skipping",
+                    executeContext.Arguments.PlayListId);
+                return executeContext.Completed();
+            }
+
+            database.PlayLists.Remove(playList);
+            await database.SaveChangesAsync(executeContext.CancellationToken);
+
+            logger.LogInformation("Deleted playlist {PlayListId} from DB", playList.Id);
+            return executeContext.Completed();
+        }
+    }
+}

Musify.Infrastructure/MassTransit/Activities/PlayLists/MarkPlayListAsRemovingActivity.cs

@@ -0,0 +1,37 @@
+using MassTransit;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using Musify.Infrastructure.MassTransit.Arguments;
+using Musify.Domain.ValueObjects;
+using Musify.Application.Contracts;
+
+namespace Musify.Infrastructure.MassTransit.Activities.PlayLists
+{
+    internal class MarkPlayListAsRemovingActivity(
+        IDatabase database,
+        ILogger<MarkPlayListAsRemovingActivity> logger)
+        : IExecuteActivity<MarkPlayListAsRemovingArguments>
+    {
+        public const string ExecuteEndpointName = "mark-playList-as-removing";
+
+        public async Task<ExecutionResult> Execute(ExecuteContext<MarkPlayListAsRemovingArguments> executeContext)
+        {
+            var playList = await database.PlayLists
+                .SingleOrDefaultAsync(p => p.Id == executeContext.Arguments.PlayListId, executeContext.CancellationToken);
+
+            if (playList is null)
+            {
+                logger.LogInformation(
+                    "PlayList {PlayListId} not found while marking as removing, skipping",
+                    executeContext.Arguments.PlayListId);
+                return executeContext.Completed();
+            }
+
+            playList.LifeCycleStatus = LifeCycleStatus.Removing;
+            await database.SaveChangesAsync(executeContext.CancellationToken);
+
+            logger.LogInformation("Marked playlist {PlayListId} as removing", playList.Id);
+            return executeContext.Completed();
+        }
+    }
+}

Musify.Infrastructure/MassTransit/Activities/PlayLists/PublishPlayListPictureProcessingEventActivity.cs

@@ -0,0 +1,34 @@
+using MassTransit;
+using Microsoft.Extensions.Logging;
+using Musify.Application.Events;
+using Musify.Infrastructure.MassTransit.Arguments;
+
+namespace Musify.Infrastructure.MassTransit.Activities.PlayLists
+{
+    internal class PublishPlayListPictureProcessingEventActivity(
+        IPublishEndpoint publishEndpoint,
+        ILogger<PublishPlayListPictureProcessingEventActivity> logger)
+        : IExecuteActivity<PublishPlayListPictureProcessingEventArguments>
+    {
+        public const string ExecuteEndpointName = "publish-playList-picture-processing-event";
+
+        public async Task<ExecutionResult> Execute(ExecuteContext<PublishPlayListPictureProcessingEventArguments> executeContext)
+        {
+            var arguments = executeContext.Arguments;
+
+            await publishEndpoint.Publish(
+                new UpdatePlayListPictureEvent(
+                    arguments.PlayListId,
+                    arguments.Bucket,
+                    arguments.FinalPictureKey,
+                    arguments.Small,
+                    arguments.Medium,
+                    arguments.Large),
+                executeContext.CancellationToken);
+
+            logger.LogInformation("Published picture processing event for playlist {PlayListId}", arguments.PlayListId);
+
+            return executeContext.Completed();
+        }
+    }
+}