fix(network): context menu on groups + group/ungroup in properties panel

Context menu fix:
- Group nodes pass pointer events through to children in React Flow, so
  right-clicking a group fires onPaneContextMenu instead of onNodeContextMenu
- handlePaneContextMenu now checks for selected nodes and shows the node
  context menu (with align/group options) when any nodes are selected

Properties panel multi-select:
- Add Group section with type dropdown (Subnet, VLAN, Site, DMZ, Custom)
- "Group into [Type]" button creates a group of the chosen type
- Ungroup button appears when a group node is in the selection
- useDiagramCommands.groupSelection now accepts a groupType param and
  uses it as the label and color key for the new group node

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

frontend/src/components/network/hooks/useDiagramCommands.ts

@@ -123,7 +123,7 @@ export function useDiagramCommands({
   const canDistribute = selectedNodes.length >= 3
 
   // ── Grouping ───────────────────────────────────────────────────────────
-  const groupSelection = useCallback(() => {
+  const groupSelection = useCallback((groupType: string = 'custom') => {
     if (selectedNodes.length < 2) return
     pushHistory(nodes, edges)
     const PADDING = 24
@@ -137,7 +137,7 @@ export function useDiagramCommands({
       type: 'group',
       position: { x: minX, y: minY },
       style: { width: maxX - minX, height: maxY - minY },
-      data: { label: 'Group', groupType: 'custom' },
+      data: { label: groupType.charAt(0).toUpperCase() + groupType.slice(1), groupType },
       selected: false,
     }
     setNodes(prev => [