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/SettingsView.swift

@@ -30,8 +30,11 @@ struct SettingsView: View {
     /// Live snapshot of the device fix + stations in range (from the monitor).
     var debugStatus: DebugLocationStatus?
     /// The app's own TOP-badge cheapest (selected fuel + stationLimit radius),
-    /// so the debug "Cheapest in range" row matches the app list exactly.
+    /// passed in so the Debug section mirrors the app list exactly.
     var appCheapest: DebugAppCheapest?
+    /// Last CoreLocation region-monitoring failure (monitor.lastRegionError).
+    /// Shown in Debug so a silently-failed geofence registration is visible.
+    var regionError: String?
 
     @StateObject private var tipStore = TipStore()
     @State private var showTipAlert = false
@@ -90,6 +93,11 @@ struct SettingsView: View {
                                 .font(.footnote)
                                 .foregroundStyle(.green)
                         }
+                        if let regionError {
+                            Label(regionError, systemImage: "exclamationmark.triangle.fill")
+                                .font(.footnote)
+                                .foregroundStyle(.red)
+                        }
                         Button {
                             onPlainTestAlert()
                         } label: {