Convert Accounts module to MediatR commands/queries

Replaces IAccountService/AccountService with one command/query per
operation, following the pattern set in the Auth module.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

mws.application/Accounts/Commands/DeleteAccount.cs

@@ -0,0 +1,34 @@
+using MediatR;
+using Mws.Application.Common;
+using Mws.Application.Permissions;
+
+namespace Mws.Application.Accounts;
+
+public record DeleteAccountCommand(Guid ActorUserId, Guid Id) : IRequest;
+
+public class DeleteAccountHandler(IUnitOfWork uow, IPermissionService permissions) : IRequestHandler<DeleteAccountCommand>
+{
+    private const string Screen = "accounts";
+
+    public async Task Handle(DeleteAccountCommand command, CancellationToken ct)
+    {
+        await permissions.EnsureAsync(command.ActorUserId, Screen, PermissionAction.Delete, ct);
+
+        var user = await uow.Users.GetByIdAsync(command.Id, ct)
+            ?? throw new NotFoundException("Account not found");
+
+        var soleOwnerProjectIds = await uow.Projects.GetOwnedProjectIdsAsync(command.Id, ct);
+
+        foreach (var projectId in soleOwnerProjectIds)
+        {
+            var ownerCount = await uow.Projects.CountOwnersAsync(projectId, ct);
+            if (ownerCount <= 1)
+            {
+                throw new BadRequestException("Cannot delete an account that is the sole owner of a project");
+            }
+        }
+
+        uow.Users.Remove(user);
+        await uow.SaveChangesAsync(ct);
+    }
+}