fix(canvas): include MAC property in approved node sent to canvas (#168)

The backend stored the MAC, but the frontend built the approved canvas
node locally with properties=[] (non-zigbee) and no mac field. On save,
canvas/save upserts every node field from the in-memory canvas, so the
empty properties overwrote the DB MAC — the address showed after a
no-save reload but vanished once saved.

Now both approve paths (single + bulk) attach a MAC property row and
the mac field to the node added to the canvas, mirroring the backend
build_mac_property. Hidden by default, toggleable from the right panel.

- new buildMacProperty util + unit tests
- bulk-approve modal test asserts MAC propagation (IP device) and
  absence for a zigbee device

ha-relevant: yes

frontend/src/utils/macProperty.ts

@@ -0,0 +1,9 @@
+import type { NodeProperty } from '@/types'
+
+/** Build the MAC address property row shown in the right panel.
+ * Hidden by default — the user opts in to showing it on the canvas card.
+ * Matches backend `build_mac_property`. Returns an empty array when no MAC. */
+export function buildMacProperty(mac?: string | null): NodeProperty[] {
+  if (!mac) return []
+  return [{ key: 'MAC', value: mac, icon: null, visible: false }]
+}