Commit MWS backend source tree

The ASP.NET Core solution (mws.api/mws.application/mws.domain/
mws.infrastructure) existed only as untracked working files. Adding
it to version control, plus a .gitignore for build output and local
tooling directories, so the CQRS/mediator refactor plan has a real
git history to branch and diff against.

mws.domain/Projects/ProjectMember.cs

@@ -0,0 +1,17 @@
+namespace Mws.Domain.Projects;
+
+public enum MemberRole
+{
+    Owner = 1,
+    Member = 2,
+}
+
+public class ProjectMember
+{
+    public Guid ProjectId { get; set; }
+    public Guid UserId { get; set; }
+    public MemberRole Role { get; set; } = MemberRole.Member;
+
+    public Project Project { get; set; } = null!;
+    public Mws.Domain.Users.User User { get; set; } = null!;
+}