Add public building project setting

docs/project-history-and-external-model-architecture.md

@@ -262,8 +262,9 @@ Completed foundation:
 - `project-device.insert` and `project-device.delete` preserve stable device
   ids; delete undo restores links only from complete unchanged disconnected-row
   snapshots in the same transaction
-- `project.update-settings` persists both project voltage defaults, its exact
-  inverse, revision and history transition atomically; the project page and
+- `project.update-settings` persists the public-building classification and
+  both project voltage defaults with their exact inverse, revision and history
+  transition atomically; the project page and
   existing PUT route require the current expected revision; the same
   transaction derives every project-device and circuit voltage again, so
   Undo/Redo cannot leave mixed voltage states