fix: network diagram editor UX — straight edges, snap-to-grid, ISP in Cloud, group resize

- Straight edges: replace SmoothStepEdge with BaseEdge + getStraightPath so
  connections draw direct diagonal lines instead of orthogonal bent paths
- Snap-to-grid: add snapToGrid/snapGrid=[20,20] to NetworkCanvas so nodes
  align consistently when dragged
- ISP in Cloud: remove standalone "Internet" sidebar section, inject ISP into
  the Cloud category loop with search support and correct item count
- Group node resize: add NodeResizer to GroupNode (subnet/VLAN/site/DMZ),
  handles visible when selected; dimensions saved/restored correctly on
  reload (also fixes group node load bug where type was always 'device')
- DiagramNode type: add nodeType and style optional fields

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

frontend/src/components/network/NetworkCanvas.tsx

@@ -85,6 +85,8 @@ export function NetworkCanvas({
         defaultEdgeOptions={{ type: 'connection' }}
         deleteKeyCode={['Backspace', 'Delete']}
         multiSelectionKeyCode="Shift"
+        snapToGrid={true}
+        snapGrid={[20, 20]}
         fitView
         className="bg-page"
       >