feat: lasso selection, multi-select panel, and named groups

- Add lasso/box selection via selectionOnDrag (Space to pan, lasso by default)
- Add lasso/pan toggle button in canvas controls (bottom-left)
- Multi-select panel in right panel when 2+ nodes selected (including zones)
- Create named Group node from selected nodes with bounding box math
- Group node: resizable, inline rename, show/hide border toggle, status summary
- GroupDetailPanel: lists members, online/offline count, ungroup action
- Fix group persistence after save/reload (extend proxmox container map to include group nodes)
- Fix groupRect serialization to preserve parent_id
- Remove background color from group and proxmox container node wrappers
- Add tests for all new store actions, GroupNode, MultiSelectPanel, GroupDetailPanel

frontend/src/components/LiveView.tsx

@@ -71,8 +71,8 @@ function LiveViewCanvas() {
         const { nodes: apiNodes, edges: apiEdges } = res.data
         const proxmoxMap = new Map<string, boolean>(
           (apiNodes as ApiNode[])
-            .filter((n: ApiNode) => n.type === 'proxmox')
-            .map((n: ApiNode) => [n.id, n.container_mode !== false])
+            .filter((n: ApiNode) => n.type === 'proxmox' || n.type === 'group')
+            .map((n: ApiNode) => [n.id, n.type === 'group' ? true : n.container_mode !== false])
         )
         loadCanvas(
           (apiNodes as ApiNode[]).map((n) => deserializeApiNode(n, proxmoxMap)),