Org units

The tenant's organisational hierarchy. Drag to reorder is a 1.x candidate; for now consumers wire `/v1/org-units/{id}/move` separately.

Pick a node from the tree on the left.

Pre-loaded branches: Njala → Freetown → Engineering and below.

Lazy-loaded branches: "Faculty of Science" and "Bo Campus". Expanding shows a per-node spinner for ~600 ms.

Recursive lazy-load: "Bo → Faculty of Agriculture" lazy-loads even though Bo itself was already lazy-loaded — the cache is per-node.