Ben-reported: picker opened on every activation. AppModel.init set region = nil and never
read UserDefaults back; saving worked, every launch forgot it. init now loads via
loadPersistedRegion() (decode + isStillValid). Selftest phase 2 writes a known region,
reloads through the same path, asserts the rect, restores the user's stored value.
Coordinator ran it: PICKER-SELFTEST PASS + REGION-PERSIST PASS, 90/90 tests green.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>