feat(network): add GroupNode component with resize, inline label, and group type colors

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/types/network-diagram.ts

@@ -123,6 +123,12 @@ export interface DiagramImportResponse {
   warnings: string[]
 }
 
+export interface GroupNodeData {
+  label: string
+  groupType: 'subnet' | 'vlan' | 'site' | 'dmz' | 'custom'
+  [key: string]: unknown
+}
+
 export interface DiagramExportResponse {
   schemaVersion: number
   name: string