feat(safety): extend Change Guard to VLAN, IP and route changes (v0.18.2-beta)

Change Guard shipped covering only 4 routes (service toggle, bond create/delete,
bridge vlan-filtering). The most recent real incident — a VLAN change that removed
a switch from management — went through PUT /:id/ports/:name/vlan, which was NOT
guarded. Neither were the bridge-VLAN CRUD routes, IP address changes, or route
changes, all of which can sever the manager's own path.

Guarded routes go from 4 to 12, adding:
- port.vlan     PUT  /:id/ports/:name/vlan      (PVID + tagged/untagged membership)
- vlan.add      POST /:id/vlans
- vlan.update   PUT  /:id/vlans/:vlanDbId
- vlan.delete   DELETE /:id/vlans/:vlanDbId
- ip.add        POST /:id/ip-addresses
- ip.remove     DELETE /:id/ip-addresses/:addrId
- route.add     POST /:id/routing
- route.remove  DELETE /:id/routing/:routeId

Each now takes a device-side restore point and arms a self-restore before applying,
disarming only once the device is proven still reachable.

Two correctness details while converting:
- vlan.delete removes the local DB row in afterConfirmed, so a change that
  auto-reverts no longer leaves the UI claiming a VLAN was deleted when the device
  restored it.
- The VLAN CRUD routes previously returned a bare array, which would have been
  spread into the guard response object. They now return a message; the frontend
  ignores these bodies and re-queries, so no client change is needed.

Verified live against the production 100G switch: a guarded VLAN add and delete
both returned protected/confirmed, were recorded in device_change_guards, and the
switch was left in its original state. 133 backend tests pass; full CI preflight green.

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

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mikrotik-manager-backend",
-  "version": "0.18.1-beta",
+  "version": "0.18.2-beta",
   "description": "Mikrotik Network Management Platform - Backend API",
   "main": "dist/index.js",
   "scripts": {