feat(network): add pointer/hand mode toggle to diagram toolbar

- Header shows MousePointer2 (select) and Hand (pan) toggle buttons
- Select mode: drag on canvas draws a selection box (selectionOnDrag)
- Pan mode: drag on canvas pans the viewport (panOnDrag)
- Space held in either mode temporarily switches to pan (panActivationKeyCode)
- Keyboard shortcuts: V = select mode, H = pan mode
- Cursor changes to grab/grabbing in pan mode

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

frontend/src/pages/NetworkDiagrams/DiagramEditor.tsx

@@ -18,7 +18,7 @@ import { NetworkCanvas } from '@/components/network/NetworkCanvas'
 import { ContextMenu, getNodeMenuActions, getCanvasMenuActions } from '@/components/network/ContextMenu'
 import { useCanvasShortcuts } from '@/components/network/hooks/useCanvasShortcuts'
 import { useDiagramCommands } from '@/components/network/hooks/useDiagramCommands'
-import { DiagramHeader } from '@/components/network/DiagramHeader'
+import { DiagramHeader, type InteractionMode } from '@/components/network/DiagramHeader'
 import { DeviceToolbar } from '@/components/network/panels/DeviceToolbar'
 import { PropertiesPanel } from '@/components/network/panels/PropertiesPanel'
 import { AIAssistPanel } from '@/components/network/panels/AIAssistPanel'
@@ -69,6 +69,8 @@ function DiagramEditorInner() {
   const [loading, setLoading] = useState(!!id)
   const [isDragOver, setIsDragOver] = useState(false)
 
+  const [interactionMode, setInteractionMode] = useState<InteractionMode>('select')
+
   const canvasRef = useRef<HTMLDivElement | null>(null)
   const [contextMenu, setContextMenu] = useState<ContextMenuState>(null)
   const [pendingDeleteNodeId, setPendingDeleteNodeId] = useState<string | null>(null)
@@ -154,6 +156,7 @@ function DiagramEditorInner() {
     onUndo: undo,
     onRedo: redo,
     onNudge,
+    onSetMode: setInteractionMode,
   })
 
   const handleNodesChange: typeof onNodesChange = useCallback((changes) => {
@@ -675,6 +678,8 @@ function DiagramEditorInner() {
         onRedo={redo}
         canUndo={canUndo}
         canRedo={canRedo}
+        interactionMode={interactionMode}
+        onModeChange={setInteractionMode}
       />
       <div className="flex flex-1 min-h-0">
         <DeviceToolbar deviceTypes={deviceTypes} onDeviceTypesChange={loadDeviceTypes} />
@@ -695,6 +700,7 @@ function DiagramEditorInner() {
               onNodeContextMenu={handleNodeContextMenu}
               onPaneContextMenu={handlePaneContextMenu}
               onPaneClick={closeContextMenu}
+              interactionMode={interactionMode}
             />
             {nodes.length === 0 && !loading && (
               <CanvasEmptyPrompt onGenerate={handleAIGenerate} />