Fix widget distance menu + geofence notification chain

Widget distance menu: the Distance picker only makes sense for
Cheapest ordering. It was hidden for Favourites but Closest still
showed it (regressed when the per-widget Distance picker was added).
parameterSummary now nests When clauses: Distance visible for
Cheapest only; Closest and Favourites hide it.

Notifications: three compounding defects kept real geofence alerts
from ever firing while the app was suspended:

1. Always permission was never properly requested. requestPermissions
   fired WhenInUse and Always back-to-back; iOS ignores the second
   call while the first prompt is pending, leaving the app stuck on
   WhenInUse — and region entries are never delivered in the
   background. Added locationManagerDidChangeAuthorization to
   ProximityMonitor: escalate WhenInUse -> Always, and re-register
   geofences on grant (regions registered under WhenInUse-only won't
   deliver in the background).

2. The 18-region window was frozen in the background. Re-registration
   lived in SwiftUI .onChange(of: locationManager.current), which
   never runs while suspended. Added a delegate hook
   (LocationManager.onLocationUpdate) fired from didUpdateLocations on
   every fix including background significant-change wake-ups; the app
   wires it to re-register geofences around the new position.

3. Region-registration failures were invisible. monitoringDidFailFor
   was never implemented, so a failed startMonitoring (region budget,
   auth, radius) silently stopped alerts. Now surfaced as
   monitor.lastRegionError and shown in Settings -> Debug; cleared on
   the next successful registration.

FuelBoard/ProximityMonitor.swift

@@ -65,6 +65,10 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
     /// Debug-only snapshot for the Settings → Debug section. Recomputed on
     /// every location/stations change via `refreshDebugStatus()`.
     @Published private(set) var debugStatus: DebugLocationStatus?
+    /// Last CoreLocation region-monitoring failure, if any. Shown in Settings
+    /// → Debug so a silently-failed `startMonitoring` (region budget exceeded,
+    /// auth not granted, radius too large) is visible instead of invisible.
+    @Published private(set) var lastRegionError: String?
 
     private let manager = CLLocationManager()
     private var stations: [FuelStation] = []
@@ -117,6 +121,10 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
 
         guard enabled else { return }
 
+        // A successful re-registration pass resets any earlier failure so the
+        // Debug section only shows the CURRENT region problem.
+        lastRegionError = nil
+
         // Favourites first (guaranteed slots), then closest stations, max 18.
         // `self.favourites` is already filtered to the monitored fuel.
         var candidates: [FuelStation] = self.favourites
@@ -198,10 +206,14 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
 
     private func requestPermissions() {
         // Region monitoring needs Always location for background delivery.
+        // Never request WhenInUse and Always back-to-back — iOS ignores the
+        // second call while the first prompt is pending, leaving the app
+        // stuck on WhenInUse and background geofence entries undelivered.
+        // Escalation happens in locationManagerDidChangeAuthorization:
+        // WhenInUse granted -> request Always -> re-register on grant.
         switch manager.authorizationStatus {
         case .notDetermined:
             manager.requestWhenInUseAuthorization()
-            manager.requestAlwaysAuthorization()
         case .authorizedWhenInUse:
             manager.requestAlwaysAuthorization()
         default:
@@ -210,6 +222,25 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
         UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { _, _ in }
     }
 
+    func locationManagerDidChangeAuthorization(_ manager: CLLocationManager) {
+        switch manager.authorizationStatus {
+        case .authorizedWhenInUse:
+            // Escalate: background region delivery (the whole point of
+            // alerts) requires Always. iOS shows the upgrade prompt here.
+            manager.requestAlwaysAuthorization()
+        case .authorizedAlways:
+            // Regions registered under WhenInUse-only won't deliver in the
+            // background; re-register now that Always is granted. (ContentView's
+            // LocationManager separately restarts significant-change tracking
+            // on its own delegate callback, so the region window follows the
+            // user in the background.)
+            update(stations: stations, favourites: FuelStore.loadFavourites(),
+                   fuel: fuel, radiusKM: radiusKM)
+        default:
+            break
+        }
+    }
+
     // MARK: - Region events
 
     nonisolated func locationManager(_ manager: CLLocationManager, didEnterRegion region: CLRegion) {
@@ -222,6 +253,20 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
         // Ignore — alerts still work while the app is open.
     }
 
+    nonisolated func locationManager(
+        _ manager: CLLocationManager,
+        monitoringDidFailFor region: CLRegion?,
+        withError error: Error
+    ) {
+        Task { @MainActor in
+            // Surface region-registration failures instead of swallowing
+            // them: a failed startMonitoring (region budget, auth, radius)
+            // means alerts silently stop. Cleared on the next successful
+            // re-registration (update() resets it).
+            lastRegionError = "\(region?.identifier ?? "?") · \(error.localizedDescription)"
+        }
+    }
+
     private func handleEntry(_ region: CLRegion) {
         let stationID = region.identifier
         // Fall back to cached data on background wake (stations may not be