feat: edge edit mode + proxmox container mode toggle

- Double-click any link to open Edit Link modal (type, label, VLAN ID, delete)
- Add updateEdge / deleteEdge actions to canvasStore
- Add container_mode field to proxmox nodes (backend model, schemas, migration)
- NodeModal shows container toggle for proxmox type (defaults ON)
- ProxmoxGroupNode renders as regular BaseNode when container_mode is OFF
- setProxmoxContainerMode store action handles structural changes atomically
  (children parentId/extent, node dimensions)
- CanvasContainer filters edges between container proxmox and its children
- Canvas load respects container_mode when assigning parentId/extent

frontend/src/types/index.ts

@@ -40,6 +40,7 @@ export interface NodeData extends Record<string, unknown> {
   response_time_ms?: number
   notes?: string
   parent_id?: string
+  container_mode?: boolean
 }
 
 export interface EdgeData extends Record<string, unknown> {