Live Activity: cheapest-in-radius Lock Screen/Dynamic Island pill

- Shared FuelBoardLiveActivityAttributes/ContentState (app + widget targets)
- FuelBoardLiveActivity Widget: ActivityConfiguration rendered by the widget
  extension - Lock Screen banner + Dynamic Island (leading/trailing/bottom,
  compact, minimal), tap anywhere -> maps:// directions to the best station
- LiveActivityManager (app side): request/update/end; mirrors the app list's
  TOP badge (selected fuel + chosen distance radius, price-then-distance
  ties); local start-date tracking for the 8h cap (this SDK's Activity has no
  startDate) - auto-restarts at 7h59m; silent no-op when disabled/denied
- Wiring: 250m/60s location hook (incl. background significant-change
  wake-ups), refresh completion, fuel/radius/unit changes, toggle flip
- Settings toggle + FuelStore persistence (keychain-backed, app-group)
- App-Info.plist: NSSupportsLiveActivities

FuelBoard/SettingsView.swift

@@ -12,6 +12,10 @@ 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. Mirrors the app list's TOP badge (selected fuel +
+    /// distance radius) and re-updates as the user drives.
+    @Binding var liveActivityEnabled: Bool
     /// 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
@@ -66,6 +70,17 @@ 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)
+                } header: {
+                    Text("Live Activity")
+                } footer: {
+                    Text("Shows the cheapest station for your selected fuel within your chosen distance on the Lock Screen and Dynamic Island. 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()