Settings About: data source section (connection, station count, GOV.UK update time)

- Relay envelope now carries source (api|csv), stations_count, and
  data_updated (freshest price_last_updated the GOV.UK server reports,
  independent of relay sync time).
- App decodes the new envelope metadata (RelayMeta), persists it after
  each full fetch, and shows it in Settings → About → Data source:
  Connection (API/CSV), Stations count, Data updated (local-formatted).
- Older relays without the fields decode cleanly (nil meta → em-dash).
- 2 new tests for meta decode + absent-meta tolerance; 37/37 pass.

Shared/FuelPriceProvider.swift

@@ -41,6 +41,21 @@ enum FuelPriceProvider {
             )
         }
     }
+
+    /// Decodes the relay envelope metadata (source, dataset update time) — the
+    /// About section shows these so the user can see which data source is
+    /// live and how fresh the GOV.UK data itself is. The fields are additive
+    /// on the relay, so older relays simply return nil values.
+    static func decodeRelayMeta(from data: Data) -> RelayMeta? {
+        guard let payload = try? JSONDecoder().decode(RelayResponse.self, from: data) else {
+            return nil
+        }
+        return RelayMeta(
+            source: payload.source,
+            stationCount: payload.stationsCount,
+            dataUpdated: payload.dataUpdated
+        )
+    }
 }
 
 // MARK: - Relay provider (default)
@@ -51,6 +66,11 @@ enum FuelPriceProvider {
 struct RelayFuelProvider: FuelPriceProviding {
     var baseURL = URL(string: "http://192.168.1.131:8789")!
 
+    /// Envelope metadata from the most recent successful relay fetch —
+    /// consumed by Settings → About (source api/csv, station count, GOV.UK
+    /// dataset update time). Written by fetchStations, read by the view.
+    static var latestMeta: RelayMeta?
+
     func fetchStations(near lat: Double?, lng: Double?, fuel: FuelType, radiusKM: Double?) async throws -> [FuelStation] {
         var components = URLComponents(url: baseURL.appendingPathComponent("api/v1/stations"), resolvingAgainstBaseURL: false)!
         var query: [URLQueryItem] = [URLQueryItem(name: "fuel", value: fuel.rawValue)]
@@ -73,11 +93,25 @@ struct RelayFuelProvider: FuelPriceProviding {
         guard let http = response as? HTTPURLResponse, http.statusCode == 200 else {
             throw FuelProviderError.relayUnavailable
         }
-        return try FuelPriceProvider.decodeStations(from: data)
+        let stations = try FuelPriceProvider.decodeStations(from: data)
+        Self.latestMeta = FuelPriceProvider.decodeRelayMeta(from: data)
+        return stations
     }
 }
 
 private struct RelayResponse: Codable {
+    /// Envelope metadata surfaced in Settings → About so the user can see
+    /// which relay source is live and how fresh the GOV.UK data is.
+    let source: String?
+    let stationsCount: Int?
+    let dataUpdated: String?
+
+    enum CodingKeys: String, CodingKey {
+        case source, stations
+        case stationsCount = "stations_count"
+        case dataUpdated = "data_updated"
+    }
+
     struct RelayStation: Codable {
         let id: String?
         let name: String?
@@ -117,6 +151,15 @@ private struct RelayResponse: Codable {
     let stations: [RelayStation]
 }
 
+/// Envelope metadata from the relay response — which data source is live
+/// (api/csv) and the freshest price-update timestamp the GOV.UK server
+/// itself reports for the dataset. Displayed in Settings → About.
+struct RelayMeta: Codable, Equatable {
+    let source: String?
+    let stationCount: Int?
+    let dataUpdated: String?
+}
+
 // MARK: - Sample provider (offline fallback only)
 
 /// Representative stations spread across ENGLAND (one cluster per region) so