- Region radius changed from fixed 300 m forecourt fence to the alert
radius (the Alerts-tab slider), clamped to the device's
maximumRegionMonitoringDistance.
- Notification now fires when you ENTER the winner's circle while
approaching, not when you reach the forecourt.
- Cheapest-gate unchanged: still only fires when the entered station is
the cheapest within the alert radius (fresh prices). Dedup still 1/
station/hour. 35 tests pass.