fix #7136: ui: tree: harmonize folder view resource ordering

Resources in the Folder View are ordered lexicographically, whereas the
Server View uses the `getTypeOrder` function for ordering.

This happens because grouping nodes in the Folder View have their `type`
property set to the literal string 'type', causing `getTypeOrder` to
return the same default value for all groups.

Fix this by resolving the actual resource type from the `groupbyid`
field in `nodeSortFn` when `type === 'type'`. This applies the defined
sort order (LXC, QEMU, Node, SDN, Network, Storage).

Signed-off-by: Elias Huhsovitz <e.huhsovitz@proxmox.com>
Link: https://lore.proxmox.com/20260818115237.91447-1-e.huhsovitz@proxmox.com