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- FuelPriceFreshness is now station-level and display-only: one age per station, fresh/outdated/unknown/invalid, "May be outdated" past 30 days, with future-tolerance and non-finite guards.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- Copy reverted from "closest eligible station" to "closest station"; stale price-confidence strings removed, "May be outdated" added.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.

FuelBoard/FavouritesView.swift

@@ -21,12 +21,10 @@ struct FavouritesView: View {
     /// still never touches the Settings default.
     let fuelSavingsSettings: FuelSavingsSettings
     @Binding var fuelSavingsAmount: FuelSavingsFillAmount
-    /// Estimated saving for a favourite, against the closest eligible station by
+    /// Estimated saving for a favourite, against the closest station by
     /// journey distance — the same baseline and definition the Stations list uses.
     var savingsForStation: (FuelStation) -> FuelSavingsAvailability? = { _ in nil }
     var journeyDiagnosticsForStation: (FuelStation) -> FuelSavingsJourneyDiagnostics? = { _ in nil }
-    var savingsPriceConfidenceForStation: (FuelStation) -> FuelPriceFreshness.ComparisonConfidence
-    var savingsPriceWarningForStation: (FuelStation) -> String? = { _ in nil }
     var onToggleFavourite: (FuelStation, FuelType) -> Void = { _, _ in }
     /// Persists a reordered favourites array (after drag-and-drop).
     var onReorder: ([FavouriteEntry]) -> Void = { _ in }
@@ -86,8 +84,6 @@ struct FavouritesView: View {
          fuelSavingsAmount: Binding<FuelSavingsFillAmount>,
          savingsForStation: @escaping (FuelStation) -> FuelSavingsAvailability? = { _ in nil },
          journeyDiagnosticsForStation: @escaping (FuelStation) -> FuelSavingsJourneyDiagnostics? = { _ in nil },
-         savingsPriceConfidenceForStation: @escaping (FuelStation) -> FuelPriceFreshness.ComparisonConfidence = { _ in .ineligible },
-         savingsPriceWarningForStation: @escaping (FuelStation) -> String? = { _ in nil },
          onToggleFavourite: @escaping (FuelStation, FuelType) -> Void = { _, _ in },
          onReorder: @escaping ([FavouriteEntry]) -> Void = { _ in },
          onHistoryUnavailable: (() -> Void)? = nil,
@@ -102,8 +98,6 @@ struct FavouritesView: View {
         _fuelSavingsAmount = fuelSavingsAmount
         self.savingsForStation = savingsForStation
         self.journeyDiagnosticsForStation = journeyDiagnosticsForStation
-        self.savingsPriceConfidenceForStation = savingsPriceConfidenceForStation
-        self.savingsPriceWarningForStation = savingsPriceWarningForStation
         self.onToggleFavourite = onToggleFavourite
         self.onReorder = onReorder
         self.onHistoryUnavailable = onHistoryUnavailable
@@ -152,7 +146,7 @@ struct FavouritesView: View {
                         Section {
                             FuelSavingsAdjustmentView(amount: $fuelSavingsAmount)
                         } footer: {
-                            Text(String(localized: "Savings below are estimated against the closest eligible station by journey distance — the same baseline as the Stations list.", comment: "Favourites fuel-savings explanation"))
+                            Text(String(localized: "Savings below are estimated against the closest station by journey distance — the same baseline as the Stations list.", comment: "Favourites fuel-savings explanation"))
                         }
                     }
 
@@ -171,8 +165,6 @@ struct FavouritesView: View {
                                 tapAction: stationTapAction,
                                 fuelSavings: savingsForStation(station),
                                 fuelSavingsAmount: fuelSavingsAmount,
-                                savingsPriceConfidence: savingsPriceConfidenceForStation(station),
-                                savingsPriceWarning: savingsPriceWarningForStation(station),
                                 onToggleFavourite: { onToggleFavourite(station, activeFuel) },
                                 onShowDetails: { detailStation = $0 }
                             )
@@ -224,8 +216,6 @@ struct FavouritesView: View {
                     selectedFuel: activeFuel,
                     fuelSavings: savingsForStation(station),
                     fuelSavingsAmount: fuelSavingsAmount,
-                    savingsPriceConfidence: savingsPriceConfidenceForStation(station),
-                    savingsPriceWarning: savingsPriceWarningForStation(station),
                     journeyDiagnostics: journeyDiagnosticsForStation(station),
                     // Every station listed here IS a favourite for the tab's
                     // fuel, so the star starts filled; tapping it unstars.