Convert Projects module to MediatR commands/queries

Replaces IProjectService/ProjectService. IProjectMemberService is
left in place for now — ProjectMembersController still depends on it
until the next task converts it too.

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

mws.application/Projects/Commands/ArchiveProject.cs

@@ -0,0 +1,24 @@
+using MediatR;
+using Mws.Application.Common;
+using Mws.Domain.Projects;
+
+namespace Mws.Application.Projects;
+
+public record ArchiveProjectCommand(Guid UserId, Guid ProjectId) : IRequest;
+
+public class ArchiveProjectHandler(IUnitOfWork uow) : IRequestHandler<ArchiveProjectCommand>
+{
+    public async Task Handle(ArchiveProjectCommand command, CancellationToken ct)
+    {
+        var project = await ProjectAccess.GetForUserOrThrowAsync(uow, command.UserId, command.ProjectId, ct);
+
+        if (await uow.Projects.GetMemberRoleAsync(command.ProjectId, command.UserId, ct) != MemberRole.Owner)
+        {
+            throw new ForbiddenException("Only the project owner can archive the project");
+        }
+
+        project.Status = ProjectStatus.Archived;
+        project.UpdatedAt = DateTime.UtcNow;
+        await uow.SaveChangesAsync(ct);
+    }
+}