feat(node-modal): restore Parent Container selector for child types

Adds back the Parent Container selector in NodeModal, shown when:
- child type is lxc or vm (parents: proxmox/vm/lxc/docker_host)
- child type is docker_container (parents: docker_host/lxc/vm/proxmox)

Selector hidden when no valid candidate node exists on the canvas.
Centralizes the parent-type allowlist in getValidParentTypes
(shared with the virtual-edge auto-parent helper).

ha-relevant: yes

frontend/src/App.tsx

@@ -550,6 +550,7 @@ export default function App() {
           onClose={() => setAddNodeOpen(false)}
           onSubmit={handleAddNode}
           title="Add Node"
+          parentCandidates={nodes.map((n) => ({ id: n.id, label: n.data.label ?? n.id, type: n.data.type }))}
         />
 
         {/* key forces re-mount when editing a different node, resetting form state */}
@@ -560,6 +561,8 @@ export default function App() {
           onSubmit={handleUpdateNode}
           initial={editNode?.data}
           title="Edit Node"
+          parentCandidates={nodes.map((n) => ({ id: n.id, label: n.data.label ?? n.id, type: n.data.type }))}
+          currentNodeId={editNodeId ?? undefined}
         />
 
         <EdgeModal