Cache-first refresh policy: auto-fetch at most twice a day (12h gate), no fetch on launch/foreground/location/fuel-switch, pull-to-refresh forces; geofences still follow location

Shared/FuelStore.swift

@@ -144,6 +144,7 @@ struct FuelStore {
     static let favouritesKey = "fuelboard.favourites"      // [FuelStation] JSON
     static let alertsEnabledKey = "fuelboard.alertsEnabled" // Bool
     static let alertsRadiusKey = "fuelboard.alertsRadius"   // Double km
+    static let lastRefreshKey = "fuelboard.lastRefresh"      // TimeInterval (seconds since 1970)
 
     // MARK: Stations
 
@@ -280,6 +281,29 @@ struct FuelStore {
         saveString(String(radius), service: alertsRadiusKey)
     }
 
+    // MARK: Refresh policy — data is cached; the app only auto-refreshes
+    // twice a day (pull-to-refresh is the manual override).
+
+    static let refreshInterval: TimeInterval = 12 * 60 * 60
+
+    static func loadLastRefresh() -> Date? {
+        if let raw = loadString(service: lastRefreshKey), let ts = TimeInterval(raw) {
+            return Date(timeIntervalSince1970: ts)
+        }
+        return nil
+    }
+
+    static func saveLastRefresh(_ date: Date = Date()) {
+        saveString(String(date.timeIntervalSince1970), service: lastRefreshKey)
+    }
+
+    /// True when the cached data is fresh enough that a scheduled auto-refresh
+    /// should be skipped (twice-a-day policy).
+    static var isCacheFresh: Bool {
+        guard let last = loadLastRefresh() else { return false }
+        return Date().timeIntervalSince(last) < refreshInterval
+    }
+
     // MARK: Low-level keychain helpers
 
     private static func keychainData(service: String) -> Data? {