Alerts tab: picker-style config matching Live Activity; move Live Activity there

- Alerts section restyled to mirror the Live Activity section: one section
  with toggle + Fuel picker + Radius picker (was segmented fuel + slider)
- Alert radius options expanded to 1/2/3/5/8/10/15/20 (display unit, snapped
  to nearest option; stored km unchanged; validation widened to 33 km)
- Live Activity section moved from Settings into the Alerts tab so both
  'notify while driving' surfaces sit together
- SettingsView loses the Live Activity bindings/section

FuelBoard/SettingsView.swift

@@ -12,14 +12,6 @@ import WidgetKit
 /// with no criteria at all.
 struct SettingsView: View {
     @Binding var distanceUnit: DistanceUnit
-    /// Whether the "cheapest nearby" Live Activity is shown on the Lock Screen
-    /// / Dynamic Island. Tracks its OWN fuel + radius (below) — independent of
-    /// the Stations tab.
-    @Binding var liveActivityEnabled: Bool
-    /// Fuel the Live Activity tracks (independent of the Stations tab).
-    @Binding var liveActivityFuel: FuelType
-    /// Search radius (miles, 5/10/15) the Live Activity uses.
-    @Binding var liveActivityRadiusMiles: Int
     /// The fuel + radius currently configured for alerts (mirrors the Alerts
     /// tab) so the test notification matches what real alerts will say.
     var alertsFuel: FuelType = .e10
@@ -74,33 +66,6 @@ struct SettingsView: View {
                     Text("Distances and search radii across the app, widget and alerts are shown in this unit.")
                 }
 
-                Section {
-                    Toggle("Live Activity", isOn: $liveActivityEnabled)
-                    Picker("Fuel", selection: $liveActivityFuel) {
-                        ForEach(FuelType.allCases) { fuel in
-                            Text(fuel.displayName).tag(fuel)
-                        }
-                    }
-                    .onChange(of: liveActivityFuel) { _, newValue in
-                        FuelStore.saveLiveActivityFuel(newValue)
-                    }
-                    Picker("Distance", selection: $liveActivityRadiusMiles) {
-                        ForEach(FuelStore.stationRadiusOptions, id: \.self) { miles in
-                            Text("\(miles) \(distanceUnit.label)").tag(miles)
-                        }
-                    }
-                    .onChange(of: liveActivityRadiusMiles) { _, newValue in
-                        FuelStore.saveLiveActivityRadiusMiles(newValue)
-                    }
-                } header: {
-                    Text("Live Activity")
-                } footer: {
-                    Text("Shows the cheapest station for the fuel and distance you pick here on the Lock Screen and Dynamic Island — independent of the Stations tab. Updates as you drive; tap to open directions. Live Activities can be disabled in System Settings → Live Activities.")
-                }
-                .onChange(of: liveActivityEnabled) { _, newValue in
-                    FuelStore.saveLiveActivityEnabled(newValue)
-                }
-
                 Section {
                     Button {
                         onShowOnboarding()