Audit shared-library source writes

A shared source goes live in every flow using it the moment it is saved, so
the write is recorded in the audit trail like a publish. Private source saves
stay drafts and are not audited.

docs/code/api.md

@@ -80,7 +80,8 @@ Function and Command nodes, changing Command settings, or changing
 `resources.env`. Other users can edit wiring, titles, and ordinary settings.
 
 Ordinary source edits stay in the draft until publishing. Shared library
-source changes affect its users immediately.
+source changes affect its users immediately, and the audit trail records them
+like a publish.
 `POST /flows/{name}/nodes/{id}/share` promotes a source to the library;
 `/unshare` makes it private again. `GET /flows/library` lists shared sources.
 `DELETE /flows/library/{name}` retires one, and answers 409 while nodes still