Sort toggle (cheapest/closest) + RAG value rating per station with TOP badge

Shared/FuelStore.swift

@@ -17,6 +17,36 @@ struct Coordinate: Equatable, Codable {
     let lng: Double
 }
 
+enum SortMode: String, Codable, CaseIterable, Identifiable {
+    case cheapest
+    case closest
+
+    var id: String { rawValue }
+
+    var displayName: String {
+        switch self {
+        case .cheapest: return "Cheapest"
+        case .closest: return "Closest"
+        }
+    }
+}
+
+/// RAG value rating for a station's price against the cheapest available.
+/// Thumb rules: within 1.5p = green (great value), within 4p = amber (okay),
+/// beyond that = red (pricey). Deliberately coarse so it reads at a glance.
+enum RAGRating: Int, Codable {
+    case green = 0
+    case amber = 1
+    case red = 2
+
+    static func rating(price: Double, cheapest: Double) -> RAGRating {
+        let delta = price - cheapest
+        if delta <= 1.5 { return .green }
+        if delta <= 4.0 { return .amber }
+        return .red
+    }
+}
+
 enum FuelType: String, Codable, CaseIterable, Identifiable {
     case e10    // Unleaded 95 (E10)
     case e5     // Premium 97/98 (E5)
@@ -72,6 +102,7 @@ struct FuelStore {
     static let stationsKey = "fuelboard.stations"      // [FuelStation] JSON
     static let locationKey = "fuelboard.lastLocation"  // "lat,lng,timestamp"
     static let fuelKey = "fuelboard.selectedFuel"      // FuelType raw value
+    static let sortModeKey = "fuelboard.sortMode"      // SortMode raw value
 
     // MARK: Stations
 
@@ -123,6 +154,19 @@ struct FuelStore {
         saveString(fuel.rawValue, service: fuelKey)
     }
 
+    // MARK: Sort mode
+
+    static func loadSortMode() -> SortMode {
+        if let raw = loadString(service: sortModeKey), let mode = SortMode(rawValue: raw) {
+            return mode
+        }
+        return .cheapest
+    }
+
+    static func saveSortMode(_ mode: SortMode) {
+        saveString(mode.rawValue, service: sortModeKey)
+    }
+
     // MARK: Low-level keychain helpers
 
     private static func keychainData(service: String) -> Data? {