feat: indicate Costco membership requirement

FuelBoard/StationNotice.swift

@@ -0,0 +1,41 @@
+import Foundation
+
+/// Presentation-only notices derived from existing station metadata.
+///
+/// These do not alter `FuelStation`, persistence, filtering, sorting, or
+/// navigation. They are intentionally small and reusable so additional
+/// informational station notices can be added later from the UI layer.
+enum StationNotice: Identifiable, Equatable {
+    case membershipRequired
+
+    var id: String {
+        switch self {
+        case .membershipRequired: return "membershipRequired"
+        }
+    }
+
+    var title: String {
+        switch self {
+        case .membershipRequired: return "Membership required"
+        }
+    }
+
+    var symbolName: String {
+        switch self {
+        case .membershipRequired: return "creditcard.fill"
+        }
+    }
+
+    static func notices(for station: FuelStation) -> [StationNotice] {
+        isCostco(station) ? [.membershipRequired] : []
+    }
+
+    static func isCostco(_ station: FuelStation) -> Bool {
+        containsCostcoToken(station.brand) || containsCostcoToken(station.name)
+    }
+
+    private static func containsCostcoToken(_ value: String) -> Bool {
+        let tokens = value.uppercased().split { !$0.isLetter && !$0.isNumber }
+        return tokens.contains("COSTCO")
+    }
+}