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/ContentView.swift

@@ -179,6 +179,16 @@ struct ContentView: View {
             // network fetch start once it's done.
             if FuelStore.loadHasCompletedOnboarding() {
                 locationManager.startForegroundTracking()
+                // Geofences must follow the user even in the background:
+                // wire the delegate hook (fires on every fix incl. background
+                // significant-change wake-ups) to re-register the region
+                // window around the new position. SwiftUI onChange alone
+                // never runs while suspended, so alerts would otherwise stay
+                // frozen around the last foreground fix.
+                locationManager.onLocationUpdate = { [weak monitor] in
+                    monitor?.update(stations: stations, favourites: refreshedFavourites,
+                                    fuel: alertsFuel, radiusKM: alertsRadius)
+                }
                 monitor.update(stations: stations, favourites: refreshedFavourites,
                                fuel: alertsFuel, radiusKM: alertsRadius)
                 monitor.setEnabled(alertsEnabled)
@@ -277,7 +287,8 @@ struct ContentView: View {
             onRefreshDebugStatus: { monitor.refreshDebugStatus() },
             onShowOnboarding: { showOnboarding = true },
             debugStatus: monitor.debugStatus,
-            appCheapest: appCheapestStatus
+            appCheapest: appCheapestStatus,
+            regionError: monitor.lastRegionError
         )
         .tabItem { Label("Settings", systemImage: "gearshape.fill") }
     }
@@ -457,6 +468,12 @@ struct StationRow: View {
 @MainActor
 final class LocationManager: NSObject, ObservableObject, @preconcurrency CLLocationManagerDelegate {
     @Published var current: Coordinate?
+    /// Called after every location fix (foreground AND background wake-ups).
+    /// The app uses it to re-register geofences around the new position —
+    /// SwiftUI's `.onChange` never runs in the background, so this delegate
+    /// hook is the only path that keeps the 18-region window following the
+    /// user while driving with the app suspended.
+    var onLocationUpdate: (() -> Void)?
     private let manager = CLLocationManager()
 
     override init() {
@@ -522,6 +539,10 @@ final class LocationManager: NSObject, ObservableObject, @preconcurrency CLLocat
             lastWidgetReload = now
             WidgetCenter.shared.reloadAllTimelines()
         }
+        // Re-register geofences around the new position. Also fires on
+        // background significant-change wake-ups, which SwiftUI onChange
+        // never sees — this is what keeps alerts working while driving.
+        onLocationUpdate?()
     }
 
     private var lastWidgetReload = Date.distantPast