feat(devices): manually add a device by MAC (offline pre-register) → 2.1.3

'+ Add by MAC' in the band header → POST /api/devices → lan_devices.addManual
(status=known, present=false; enriched on next scan). Repo + API + frontend tests.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "void-server",
-  "version": "2.1.2",
+  "version": "2.1.3",
   "type": "module",
   "private": true,
   "scripts": {