Make station price age informational only

The relay's price_updated is the maximum price_last_updated across the grades it maps, so it cannot vouch for the selected grade: stop using it to score, gate or warn about Best Value.

- FuelPriceFreshness is now station-level and display-only: one age per station, fresh/outdated/unknown/invalid, "May be outdated" past 30 days, with future-tolerance and non-finite guards.
- Best Value restores the closest-station-selling-the-selected-fuel baseline and its savings ranking; eligibility gating, eligible-first sorting and the unavailable banner are gone.
- Price age appears in the More info sheet only - no listing-row warnings, no extra banners.
- Copy reverted from "closest eligible station" to "closest station"; stale price-confidence strings removed, "May be outdated" added.
- Dormant per-grade timestamp plumbing removed, and regression tests added for every fuel type, missing/invalid/future stamps and the bundled offline dump.

Shared/FuelPriceProvider.swift

@@ -38,9 +38,7 @@ enum FuelPriceProvider {
                 lat: relay.lat ?? 0,
                 lng: relay.lng ?? 0,
                 prices: relay.allPrices,
-                    priceUpdated: relay.priceUpdatedDate?.timeIntervalSince1970,
-                    priceUpdatedByFuel: relay.priceUpdatedByFuel,
-                    priceUpdatedByFuelRaw: relay.priceUpdatedByFuelRaw
+                priceUpdated: relay.priceUpdatedDate?.timeIntervalSince1970
             )
         }
     }
@@ -118,41 +116,16 @@ private struct MirrorResponse: Codable {
         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:
         /// any grade outside the 50–500 pence/litre band is dropped, so a mirror