Best Value: baseline on the closest eligible price and gate on freshness

- Add FuelPriceFreshness: selected-fuel-aware eligibility plus a shared
  comparison confidence, so a saving is presented as verified only when
  both the candidate and the baseline pass the gate for the fuel on screen.
- Rank against the closest station with an eligible selected-fuel price
  instead of the physically closest station, so a single stale neighbour
  can no longer invalidate every comparison in the list. Ordinary Closest
  sorting still includes every priced station.
- Keep ineligible prices visible, fall back to pump-price order, and label
  Best Value unavailable when no comparison qualifies.
- Widget: same baseline and confidence path as the app.
- Tests: stale-closest baseline, alert baseline, eligibility policy,
  boundary and missing-timestamp regressions.

Shared/FuelPriceProvider.swift

@@ -38,7 +38,9 @@ enum FuelPriceProvider {
                 lat: relay.lat ?? 0,
                 lng: relay.lng ?? 0,
                 prices: relay.allPrices,
-                priceUpdated: nil
+                    priceUpdated: relay.priceUpdatedDate?.timeIntervalSince1970,
+                    priceUpdatedByFuel: relay.priceUpdatedByFuel,
+                    priceUpdatedByFuelRaw: relay.priceUpdatedByFuelRaw
             )
         }
     }
@@ -65,6 +67,15 @@ enum FuelPriceProvider {
         return result
     }
 
+    static func fuelType(for grade: String) -> FuelType? {
+        switch grade.uppercased() {
+        case "E10": return .e10
+        case "E5": return .e5
+        case "DIESEL", "B7", "B7S", "B7P", "B10": return .diesel
+        default: return nil
+        }
+    }
+
     /// Decodes mirror 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
@@ -106,6 +117,41 @@ private struct MirrorResponse: Codable {
         let lng: Double?
         let price: Double?
         let prices: [String: Double]?
+        let priceUpdated: String?
+        let priceUpdatedByGrade: [String: String]?
+        let priceUpdatedByFuelRawValues: [String: String]?
+
+        enum CodingKeys: String, CodingKey {
+            case id, name, brand, address, postcode, lat, lng, price, prices
+            case priceUpdated = "price_updated"
+            case priceUpdatedByGrade = "price_updated_by_grade"
+            case priceUpdatedByFuelRawValues = "price_updated_by_fuel"
+        }
+
+        var priceUpdatedDate: Date? {
+            FuelPriceTimestamp.parse(priceUpdated)
+        }
+
+        var priceUpdatedByFuelRaw: [FuelType: String]? {
+            let raw = priceUpdatedByGrade ?? priceUpdatedByFuelRawValues
+            guard let raw else { return nil }
+            let parsed = raw.reduce(into: [FuelType: String]()) { result, item in
+                guard let fuel = FuelPriceProvider.fuelType(for: item.key) else { return }
+                result[fuel] = item.value
+            }
+            return parsed.isEmpty ? nil : parsed
+        }
+
+        var priceUpdatedByFuel: [FuelType: TimeInterval]? {
+            let raw = priceUpdatedByGrade ?? priceUpdatedByFuelRawValues
+            guard let raw else { return nil }
+            let parsed = raw.reduce(into: [FuelType: TimeInterval]()) { result, item in
+                guard let fuel = FuelPriceProvider.fuelType(for: item.key),
+                      let date = FuelPriceTimestamp.parse(item.value) else { return }
+                result[fuel] = date.timeIntervalSince1970
+            }
+            return parsed.isEmpty ? nil : parsed
+        }
 
         /// Map mirror grade keys (E5/E10/DIESEL) to FuelType for ALL fuels the
         /// station sells — one fetch populates every fuel tab. Defensive guard: