Add "View Networks": front-facing subnet browse + detail with attached devices

Subnets previously lived only under Settings, easily confused with the Network
Devices asset list. Add a front-facing browse + detail:

- Nav: rename "Network" -> "Network Devices"; add "View Networks" (subnets), both
  under Assets (network plugin get_navigation_items; frontend fallback matched).
- /networks (SubnetsBrowse): all subnets with name / CIDR / type / VLAN / notes,
  searchable, row-click to detail.
- /networks/:id (SubnetDetail): the subnet (CIDR, network address, type, VLAN,
  gateway, notes) plus the network devices whose primary IP falls inside its
  CIDR - get_subnet now computes that membership in Python (a device's IP lives
  in a Communication row, so it is not a plain SQL join).

Verified on the import DB: 37 networks list (real WJ subnets), detail renders.

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

frontend/src/router/routes/network.js

@@ -26,6 +26,18 @@ export default [
     component: () => import('../../views/network/NetworkDeviceForm.vue'),
     meta: { requiresAuth: true, plugin: 'network' }
   },
+  {
+    path: 'networks',
+    name: 'networks',
+    component: () => import('../../views/network/SubnetsBrowse.vue'),
+    meta: { plugin: 'network' }
+  },
+  {
+    path: 'networks/:id',
+    name: 'network-subnet-detail',
+    component: () => import('../../views/network/SubnetDetail.vue'),
+    meta: { plugin: 'network' }
+  },
   // Network-specific settings
   {
     path: 'settings/vlans',