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/__tests__/macProperty.test.ts

@@ -0,0 +1,16 @@
+import { describe, it, expect } from 'vitest'
+import { buildMacProperty } from '../macProperty'
+
+describe('buildMacProperty', () => {
+  it('returns a hidden MAC property row for a MAC', () => {
+    expect(buildMacProperty('aa:bb:cc:dd:ee:ff')).toEqual([
+      { key: 'MAC', value: 'aa:bb:cc:dd:ee:ff', icon: null, visible: false },
+    ])
+  })
+
+  it('returns an empty array when MAC is null/undefined/empty', () => {
+    expect(buildMacProperty(null)).toEqual([])
+    expect(buildMacProperty(undefined)).toEqual([])
+    expect(buildMacProperty('')).toEqual([])
+  })
+})