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>

plugins/network/plugin.py

@@ -208,11 +208,17 @@ class NetworkPlugin(BasePlugin):
         """Return navigation menu items."""
         return [
             {
-                'name': 'Network',
+                'name': 'Network Devices',
                 'icon': 'network-wired',
                 'route': '/network',
                 'position': 18,
             },
+            {
+                'name': 'View Networks',
+                'icon': 'globe',
+                'route': '/networks',
+                'position': 19,
+            },
         ]
 
     def get_permissions(self) -> List: