Favourites tab: fuel-type selector gets the same coloured pump icons

- FuelTypeSegmentedPicker promoted to shared (was private in StationsView)
  and parameterised by fuel list so Favourites passes only fuels with favourites
- Favourites tab swaps native .segmented picker for the capsule control with
  green/purple/grey fuelpump icons, matching Stations

FuelBoard/FavouritesView.swift

@@ -84,12 +84,10 @@ struct FavouritesView: View {
                     }
                 } else {
                     Section("Fuel type") {
-                        Picker("Fuel type", selection: $fuel) {
-                            ForEach(availableFuels) { fuel in
-                                Text(fuel.shortName).tag(fuel)
-                            }
-                        }
-                        .pickerStyle(.segmented)
+                        FuelTypeSegmentedPicker(
+                            selection: $fuel,
+                            fuels: availableFuels
+                        )
                     }
 
                     Section("\(activeFuel.displayName) favourites — cheapest first") {

FuelBoard/StationsView.swift

@@ -204,14 +204,18 @@ extension FuelType {
 /// Fuel-type selector styled like a segmented control, with a coloured pump
 /// icon per fuel (green = unleaded, purple = premium, grey = diesel). Built
 /// custom because the native `.segmented` picker tints every segment the same
-/// accent colour — it can't show per-fuel pump colours.
-private struct FuelTypeSegmentedPicker: View {
+/// accent colour — it can't show per-fuel pump colours. Shared by the Stations
+/// and Favourites tabs.
+struct FuelTypeSegmentedPicker: View {
     @Binding var selection: FuelType
-    var onSelect: (FuelType) -> Void
+    /// Which fuels to show. Defaults to all; the Favourites tab passes only
+    /// the fuels that actually have favourites.
+    var fuels: [FuelType] = FuelType.allCases
+    var onSelect: (FuelType) -> Void = { _ in }
 
     var body: some View {
         HStack(spacing: 3) {
-            ForEach(FuelType.allCases) { fuel in
+            ForEach(fuels) { fuel in
                 let isSelected = fuel == selection
                 Button {
                     selection = fuel