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.

.gitignore

@@ -0,0 +1,7 @@
+bin/
+obj/
+.vs/
+.idea/
+.DS_Store
+.claude/
+.serena/