v0.10.1 — build_backend cleans up after itself

Fixed

• build_backend no longer leaves a half-built project behind. When the plan does not allow another published app it says so before creating anything, and if any later step fails it removes the project and the app it made instead of naming them in an error message.

Server-side fixes shipped the same day and need no client update: links made when a row is created are now written to the relation graph, a deleted row never comes back as a live link, and a required column cannot be emptied through any channel.