feat: station tap action toggle (open map vs more info)

Settings → Units gains a Tap station picker: Open map (default,
historic behaviour — tap opens Apple Maps directions) or More info
(tap shows a detail sheet with name, address, distance from current
location, and a Directions button). Applies to Stations and
Favourites tabs; persisted keychain-first as
fuelboard.stationTapAction. Stations footer hint follows the setting.

FuelBoard/FavouritesView.swift

@@ -14,6 +14,7 @@ struct FavouritesView: View {
     let location: Coordinate?
     let distanceUnit: DistanceUnit
     let priceDisplayStyle: PriceDisplayStyle
+    let stationTapAction: StationTapAction
     var onToggleFavourite: (FuelStation, FuelType) -> Void = { _, _ in }
     /// Persists a reordered favourites array (after drag-and-drop).
     var onReorder: ([FavouriteEntry]) -> Void = { _ in }
@@ -37,6 +38,9 @@ struct FavouritesView: View {
     /// Trends sheet (price history chart) presentation state.
     @State private var showTrends = false
 
+    /// Station picked for the More-info sheet (tap action = showDetails).
+    @State private var detailStation: FuelStation?
+
     private var activeFuel: FuelType {
         availableFuels.contains(fuel) ? fuel : (availableFuels.first ?? .e10)
     }
@@ -65,6 +69,7 @@ struct FavouritesView: View {
          location: Coordinate?,
          distanceUnit: DistanceUnit,
          priceDisplayStyle: PriceDisplayStyle,
+         stationTapAction: StationTapAction,
          onToggleFavourite: @escaping (FuelStation, FuelType) -> Void = { _, _ in },
          onReorder: @escaping ([FavouriteEntry]) -> Void = { _ in },
          onHistoryUnavailable: (() -> Void)? = nil,
@@ -74,6 +79,7 @@ struct FavouritesView: View {
         self.location = location
         self.distanceUnit = distanceUnit
         self.priceDisplayStyle = priceDisplayStyle
+        self.stationTapAction = stationTapAction
         self.onToggleFavourite = onToggleFavourite
         self.onReorder = onReorder
         self.onHistoryUnavailable = onHistoryUnavailable
@@ -129,7 +135,9 @@ struct FavouritesView: View {
                                 baselinePrice: cheapestPrice,
                                 isTopResult: index == 0,
                                 isFavourite: activeFuelFavouriteIDs.contains(station.id),
-                                onToggleFavourite: { onToggleFavourite(station, activeFuel) }
+                                tapAction: stationTapAction,
+                                onToggleFavourite: { onToggleFavourite(station, activeFuel) },
+                                onShowDetails: { detailStation = $0 }
                             )
                         }
                         .onMove(perform: moveFavourite)
@@ -171,6 +179,13 @@ struct FavouritesView: View {
                     onHistoryRecovered: onHistoryRecovered
                 )
             }
+            .sheet(item: $detailStation) { station in
+                StationDetailView(
+                    station: station,
+                    location: location,
+                    distanceUnit: distanceUnit
+                )
+            }
             .onAppear {
 #if DEBUG
                 // QA hook: launch with `-showTrends` to open the sheet