Add optional room areas

docs/circuit-list-editor-api.md

@@ -67,6 +67,12 @@ Prüfsumme; Ersetzen übernimmt die Grobbilanzen atomar und mit Undo/Redo,
 Duplizieren vergibt neue IDs. Transferformat 1 bleibt ohne Grobbilanzen
 importierbar.
 
+Das aktuelle Projekt-Snapshot-Schema 8 enthält außerdem die optionale
+Netto-Raumfläche `rooms[].areaM2`. Snapshot-Versionen 1–7 werden dafür mit
+`areaM2 = null` hochgestuft. Restore, Export und Import erhalten vorhandene
+Flächen; eine eigene Transferformat-Version ist nicht nötig, weil Format 2 den
+versionierten Projektsnapshot einbettet.
+
 The public dispatcher supports the Circuit and CircuitDeviceRow commands
 `circuit.update`, `circuit.insert`, `circuit.delete`,
 `circuit-device-row.update`, `circuit-device-row.insert`,
@@ -297,19 +303,26 @@ commands. Endpoints, payloads and calculation rules: `docs/estimate-balance.md`.
   - rejects floors with assigned rooms or distribution boards
 - `POST /projects/:projectId/rooms`
   - body:
-    `{ "floorId": "floor_1", "roomNumber": "001", "roomName": "Technik", "expectedRevision": 14 }`
-  - executes `project-room.insert` with a stable room id; `floorId` is optional
-    and must belong to the project when present
+    `{ "floorId": "floor_1", "roomNumber": "001", "roomName": "Technik", "areaM2": 18.75, "expectedRevision": 14 }`
+  - executes `project-room.insert` command version 2 with a stable room id;
+    `floorId` and `areaM2` are optional. An omitted or explicit `null` area
+    creates a room without area; a value must be finite and non-negative.
   - response: `{ "room": { ... }, "revision": { ... }, "history": { ... } }`
 - `PUT /projects/:projectId/rooms/:roomId`
   - body:
-    `{ "floorId": null, "roomNumber": "101", "roomName": "Büro", "expectedRevision": 16 }`
-  - updates number, name and optional floor as one persistent command
+    `{ "floorId": null, "roomNumber": "101", "roomName": "Büro", "areaM2": null, "expectedRevision": 16 }`
+  - updates number, name, optional floor and area as one persistent version-2
+    command. If `areaM2` is omitted, the current area is retained; `null`
+    explicitly clears it.
 - `DELETE /projects/:projectId/rooms/:roomId`
   - body: `{ "expectedRevision": 17 }`
   - rejects rooms referenced by device rows
 - Persistent Undo/Redo restores exact previous and target records without
   silently clearing foreign keys.
+- Stored version-1 room commands remain executable and are upgraded with
+  `areaM2 = null`. Exact expected-record checks reject an old update or delete
+  if a newer command has added an area, so legacy history cannot silently
+  erase it.
 - Stale revisions return `409 PROJECT_REVISION_CONFLICT`.
 
 ### Tree Endpoint