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- FuelPriceFreshness is now station-level and display-only: one age per station, fresh/outdated/unknown/invalid, "May be outdated" past 30 days, with future-tolerance and non-finite guards.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- Copy reverted from "closest eligible station" to "closest station"; stale price-confidence strings removed, "May be outdated" added.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

@@ -20,8 +20,6 @@ struct StationsView: View {
     @Binding var fuelSavingsAmount: FuelSavingsFillAmount
     var savingsForStation: (FuelStation) -> FuelSavingsAvailability? = { _ in nil }
     var journeyDiagnosticsForStation: (FuelStation) -> FuelSavingsJourneyDiagnostics? = { _ in nil }
-    var savingsPriceConfidenceForStation: (FuelStation) -> FuelPriceFreshness.ComparisonConfidence
-    var savingsPriceWarningForStation: (FuelStation) -> String?
     var onToggleFavourite: (FuelStation, FuelType) -> Void = { _, _ in }
     var onRefresh: () async -> Void = {}
 
@@ -123,11 +121,6 @@ struct StationsView: View {
                     // for a switched-off feature.
                     if sortMode == .worthTheDrive && fuelSavingsSettings.isConfigured {
                         FuelSavingsAdjustmentView(amount: $fuelSavingsAmount)
-                        if !stations.isEmpty && stations.allSatisfy({ savingsPriceConfidenceForStation($0) == .ineligible }) {
-                            Text("Best Value unavailable: no eligible price comparison. Stations and prices remain visible below.")
-                                .font(.caption)
-                                .foregroundStyle(.orange)
-                        }
                     }
 
                     if isLoading && stations.isEmpty {
@@ -264,8 +257,6 @@ struct StationsView: View {
             selectedFuel: selectedFuel,
             fuelSavings: savingsForStation(station),
             fuelSavingsAmount: fuelSavingsAmount,
-            savingsPriceConfidence: savingsPriceConfidenceForStation(station),
-            savingsPriceWarning: savingsPriceWarningForStation(station),
             journeyDiagnostics: journeyDiagnosticsForStation(station),
             isFavourite: favouriteIDs.contains(station.id),
             onToggleFavourite: { onToggleFavourite(station, selectedFuel) }
@@ -369,8 +360,6 @@ struct StationsView: View {
             tapAction: stationTapAction,
             fuelSavings: savingsForStation(station),
             fuelSavingsAmount: fuelSavingsAmount,
-            savingsPriceConfidence: savingsPriceConfidenceForStation(station),
-            savingsPriceWarning: savingsPriceWarningForStation(station),
             onToggleFavourite: { onToggleFavourite(station, selectedFuel) },
             onShowDetails: { detailStation = $0 }
         )