Tombstone a project's workrooms while Delete Project tears down its remote hosts #287

🤖 Left by Claude Code, from the pre-landing review of #253.

AppStore.deleteProject removes the project from the sidebar optimistically, then tears down each remote workroom and the base before calling delete-project. That can take minutes (a docker rm, a grant cancel and a config write per workroom). Unlike deleteWorkroom, nothing tombstones the project or its workrooms meanwhile, so any reload() in that window (another window's create, a failed delete) republishes the project with half-destroyed remote workrooms. The user can then open panes on them or start a second delete.

Fix: tombstone the project's workrooms (deletingWorkrooms) and the project path for the duration, as deleteWorkroom does.

Related: #253.