Live Activity: own fuel + distance config, independent of Stations tab

- Settings → Live Activity now has Fuel and Distance pickers (5/10/15,
  unit-aware) stored under fuelboard.liveActivityFuel / liveActivityRadiusMiles
- LiveActivityManager uses these instead of the Stations-tab selectedFuel /
  stationLimit; Stations changes no longer re-target the pill
- Fuel moved from Activity attributes into ContentState so changing fuel in
  Settings updates the RUNNING activity in place (no end+restart needed)
- Stations tab stays a pure data-interrogation + favourites surface

FuelBoardWidgets/FuelBoardLiveActivityView.swift

@@ -55,7 +55,7 @@ private struct FuelBoardLiveActivityView: View {
 
                 // MIDDLE — fuel + station
                 VStack(alignment: .leading, spacing: 2) {
-                    Text("Cheapest \(context.attributes.fuel.displayName)")
+                    Text("Cheapest \(context.state.fuel.displayName)")
                         .font(.headline)
                     Text("\(context.state.stationName) · \(context.state.distanceText)")
                         .font(.subheadline)
@@ -94,7 +94,7 @@ private struct FuelBoardLiveActivityCompactView: View {
 
     var body: some View {
         VStack(alignment: .leading, spacing: 2) {
-            Text("Cheapest \(context.attributes.fuel.displayName)")
+            Text("Cheapest \(context.state.fuel.displayName)")
                 .font(.caption2)
                 .foregroundStyle(.secondary)
             Text(context.state.stationName)