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

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

Musify.Application/Users/Commands/CreateUserCommand.cs

@@ -0,0 +1,26 @@
+using Ardalis.Result;
+using Mediator;
+using Musify.Application.Users.Responses;
+using Musify.Domain.Entities;
+
+namespace Musify.Application.Users.Commands
+{
+    public record CreateUserCommand(long Id,
+        string Name,
+        string? FirstName,
+        string? SecondName)
+        : ICommand<Result<UserApplicationResponse>>
+    {
+        public static User ToEntity(CreateUserCommand command)
+        {
+            return new User
+            {
+                Id = command.Id,
+                Name = command.Name,
+                NormalizedName = command.Name.ToUpperInvariant(),
+                FirstName = command.FirstName,
+                SecondName = command.SecondName
+            };
+        }
+    }
+}

Musify.Application/Users/Commands/SyncUserCommand.cs

@@ -0,0 +1,13 @@
+using Ardalis.Result;
+using Mediator;
+
+namespace Musify.Application.Users.Commands
+{
+    public record SyncUserCommand(
+        long Id,
+        string Name,
+        string? FirstName,
+        string? SecondName,
+        string? ProfilePictureUrl)
+        : ICommand<Result>;
+}

Musify.Application/Users/Handlers/CreateUserCommandHandler.cs

@@ -0,0 +1,40 @@
+using Ardalis.Result;
+using Mediator;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using Musify.Application.Contracts;
+using Musify.Application.Users.Commands;
+using Musify.Application.Users.Responses;
+
+namespace Musify.Application.Users.Handlers
+{
+    public class CreateUserCommandHandler(IDatabase database, ILogger<CreateUserCommandHandler> logger)
+        : ICommandHandler<CreateUserCommand, Result<UserApplicationResponse> >
+    {
+        public async ValueTask<Result<UserApplicationResponse>> Handle(CreateUserCommand request, CancellationToken cancellationToken)
+        {
+            var userExists = await database.Users.AnyAsync(u => u.Id == request.Id, cancellationToken);
+            if (userExists)
+            {
+                logger.LogInformation("User {UserId} already exists", request.Id);
+                return Result<UserApplicationResponse>.Conflict($"User {request.Id} already exists");
+            }
+
+            var newUser = CreateUserCommand.ToEntity(request);
+
+            try
+            {
+                await database.Users.AddAsync(newUser, cancellationToken);
+                await database.SaveChangesAsync(cancellationToken);
+            }
+            catch (Exception exception)
+            {
+                logger.LogError(exception, "Failed to create user {UserId}", request.Id);
+                return Result.Error($"Failed to create user {request.Id}");
+            }
+
+            logger.LogInformation("Created user {UserId}", newUser.Id);
+            return Result.Created(UserApplicationResponse.FromEntity(newUser));
+        }
+    }
+}

Musify.Application/Users/Handlers/GetUserByIdQueryHandler.cs

@@ -0,0 +1,26 @@
+using Ardalis.Result;
+using Mediator;
+using Microsoft.EntityFrameworkCore;
+using Musify.Application.Contracts;
+using Musify.Application.Users.Queries;
+using Musify.Application.Users.Responses;
+
+namespace Musify.Application.Users.Handlers
+{
+    public class GetUserByIdQueryHandler(IDatabase database)
+        : IQueryHandler<GetUserByIdQuery, Result<UserApplicationResponse> >
+    {
+        public async ValueTask<Result<UserApplicationResponse>> Handle(GetUserByIdQuery request, CancellationToken cancellationToken)
+        {
+            var user = await database.Users
+                .AsNoTracking()
+                .Where(u => u.Id == request.Id)
+                .Select(u => UserApplicationResponse.FromEntity(u))
+                .SingleOrDefaultAsync(cancellationToken);
+
+            return user is null
+                ? Result<UserApplicationResponse>.NotFound()
+                : Result.Success(user);
+        }
+    }
+}

Musify.Application/Users/Handlers/GetUsersQueryHandler.cs

@@ -0,0 +1,35 @@
+using Ardalis.Result;
+using Mediator;
+using Microsoft.EntityFrameworkCore;
+using Musify.Application.Pagination;
+using Musify.Application.Users.Queries;
+using Musify.Application.Users.Responses;
+using X.PagedList.EF;
+using Musify.Application.Contracts;
+
+namespace Musify.Application.Users.Handlers
+{
+    public class GetUsersQueryHandler(IDatabase database)
+        : IQueryHandler<GetUsersQuery, Result<PaginatedResponse<UserApplicationResponse> > >
+    {
+        public async ValueTask<Result<PaginatedResponse<UserApplicationResponse> >> Handle(GetUsersQuery request, CancellationToken cancellationToken)
+        {
+            var user = database.Users
+                .AsNoTracking()
+                .AsQueryable();
+
+            if (request.UsernameSearch is not null)
+            {
+                var normalizedUsername = request.UsernameSearch.Trim().ToUpperInvariant();
+                user = user.Where(u => u.NormalizedName.Contains(normalizedUsername));
+            }
+
+            var totalCount = await user.CountAsync(cancellationToken);
+            var pagedUser = await user
+                .Select(u => UserApplicationResponse.FromEntity(u))
+                .ToPagedListAsync(request.PageNumber, request.PageSize, totalCount, cancellationToken);
+
+            return Result.Success(PaginatedResponse<UserApplicationResponse>.FromPagedList(pagedUser));
+        }
+    }
+}

Musify.Application/Users/Handlers/SyncUserCommandHandler.cs

@@ -0,0 +1,50 @@
+using Ardalis.Result;
+using Mediator;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using Musify.Application.Contracts;
+using Musify.Application.Users.Commands;
+using Musify.Domain.Entities;
+
+namespace Musify.Application.Users.Handlers
+{
+    public class SyncUserCommandHandler(IDatabase database, ILogger<SyncUserCommandHandler> logger)
+        : ICommandHandler<SyncUserCommand, Result>
+    {
+        public async ValueTask<Result> Handle(SyncUserCommand request, CancellationToken cancellationToken)
+        {
+            var user = await database.Users
+                .SingleOrDefaultAsync(u => u.Id == request.Id, cancellationToken);
+
+            if (user is null)
+            {
+                await database.Users.AddAsync(new User
+                {
+                    Id = request.Id,
+                    Name = request.Name,
+                    NormalizedName = request.Name.ToUpperInvariant(),
+                    FirstName = request.FirstName,
+                    SecondName = request.SecondName,
+                    ProfilePictureUrl = request.ProfilePictureUrl
+                }, cancellationToken);
+
+                await database.SaveChangesAsync(cancellationToken);
+                logger.LogInformation("Provisioned user {UserId}", request.Id);
+
+                return Result.Success();
+            }
+
+            user.Name = request.Name;
+            user.NormalizedName = request.Name.ToUpperInvariant();
+            user.FirstName = request.FirstName;
+            user.SecondName = request.SecondName;
+            user.ProfilePictureUrl = request.ProfilePictureUrl;
+
+            var written = await database.SaveChangesAsync(cancellationToken);
+            if (written > 0)
+                logger.LogInformation("Synced profile for user {UserId}", request.Id);
+
+            return Result.Success();
+        }
+    }
+}

Musify.Application/Users/Queries/GetUserByIdQuery.cs

@@ -0,0 +1,9 @@
+using Ardalis.Result;
+using Mediator;
+using Musify.Application.Users.Responses;
+
+namespace Musify.Application.Users.Queries
+{
+    public record GetUserByIdQuery(long Id)
+        : IQuery<Result<UserApplicationResponse> >;
+}

Musify.Application/Users/Queries/GetUsersQuery.cs

@@ -0,0 +1,10 @@
+using Ardalis.Result;
+using Mediator;
+using Musify.Application.Pagination;
+using Musify.Application.Users.Responses;
+
+namespace Musify.Application.Users.Queries
+{
+    public record GetUsersQuery(int PageNumber, int PageSize, string? UsernameSearch = null)
+        : IQuery<Result<PaginatedResponse<UserApplicationResponse> >>;
+}

Musify.Application/Users/Responses/UserApplicationResponse.cs

@@ -0,0 +1,26 @@
+using Musify.Domain.Entities;
+
+namespace Musify.Application.Users.Responses
+{
+    public record UserApplicationResponse(
+        long Id,
+        string Name,
+        string? FirstName,
+        string? SecondName,
+        string? ProfilePictureUrl,
+        DateTime CreatedAt,
+        DateTime UpdatedAt)
+    {
+        public static UserApplicationResponse FromEntity(User user)
+        {
+            return new UserApplicationResponse(
+                user.Id,
+                user.Name,
+                user.FirstName,
+                user.SecondName,
+                user.ProfilePictureUrl,
+                user.CreatedAt,
+                user.UpdatedAt);
+        }
+    }
+}