Reorganize vehicle groups more reliably in Settings

Several fixes to the group hierarchy manager make moving, deleting, and viewing groups behave the way the page describes.

Before you start

You'll need access to Settings > Groups.

Steps

1. Go to Settings > Groups.
2. Drag a group out from under its parent to promote it to the top level — it now moves, instead of silently staying put.
3. Delete a group that still holds a vehicle — the confirmation dialog now matches what actually happens.

Result / verify

After moving a group, its position and its subtree's place in the hierarchy update correctly. Group and vehicle counts on the KPI tiles reconcile with what's actually in each group.