feat: edit container parent in the node modal instead of detail panel

Replaces the detail-panel container selector with the existing "Parent
Container" dropdown in the edit modal (double-click). The selector now
shows for any node that is nested in — or can nest into — a container_mode
node, not just lxc/vm/docker_container, so a dragged-in node can be
re-targeted or detached ("None") from the modal.

- NodeModal: container_mode candidates count as valid parents; selector
  shown for nested nodes; submit/type-change keep valid container parents
- App: pass container_mode in parentCandidates
- revert detail-panel selector + setNodeParent store action (updateNode
  already handles parent attach/detach)

ha-relevant: yes

frontend/src/App.tsx

@@ -650,7 +650,7 @@ 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 }))}
+          parentCandidates={nodes.map((n) => ({ id: n.id, label: n.data.label ?? n.id, type: n.data.type, container_mode: n.data.container_mode }))}
         />
 
         {/* key forces re-mount when editing a different node, resetting form state */}
@@ -677,7 +677,7 @@ export default function App() {
             }
             return nodes
               .filter((n) => !descendants.has(n.id))
-              .map((n) => ({ id: n.id, label: n.data.label ?? n.id, type: n.data.type }))
+              .map((n) => ({ id: n.id, label: n.data.label ?? n.id, type: n.data.type, container_mode: n.data.container_mode }))
           })()}
           currentNodeId={editNodeId ?? undefined}
         />