Update Scale Region

Rename (metadata-only) and/or move/resize a region.

A geometry change re-resolves membership and recomputes (spec §5.4). If the edit would straddle or strand any measurement, the route rejects 422 ("scale_region_edit_would_orphan_measurements") unless on_orphan selects an explicit resolution: 'snap_to_page' (only valid when a page scale exists) or 'delete'.

Returned by calibrate / edit / delete: the region (omitted on delete is out of scope — delete returns only the count) plus how many measurements were recomputed in the same transaction.