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/FuelPriceWidgetViews.swift

@@ -35,6 +35,11 @@ struct FuelPriceWidgetEntryData {
     let locationSource: String    // "live" | "cached" | "none"
     let unit: DistanceUnit        // user's display unit for distances
     let bestValueResult: FuelSavingsResult? // only populated for the small Best Value face
+    /// Both selected-fuel prices are assessed by the shared freshness policy.
+    var bestValuePriceConfidence: FuelPriceFreshness.ComparisonConfidence = .ineligible
+    /// Candidate-aware warning copy (names the fuel, and the baseline when the
+    /// baseline is the weak link). Falls back to the confidence's own text.
+    var bestValuePriceWarning: String? = nil
 }
 
 /// The widget face, parameterised by family so the app can preview it.
@@ -92,10 +97,31 @@ struct FuelPriceWidgetContent: View {
                 Text(result.headline(compact: true))
                     .font(.title3.weight(.bold))
                     .lineLimit(1)
-                Text(result.status == .baseline ? "your baseline" : "vs closest station")
+                Text(result.status == .baseline ? "your baseline" : "vs closest eligible station")
                     .font(.caption2)
                     .foregroundStyle(.secondary)
                     .lineLimit(1)
+                if let warning = entry.bestValuePriceWarning ?? entry.bestValuePriceConfidence.warningText {
+                    Text(warning)
+                        .font(.caption2)
+                        .foregroundStyle(.orange)
+                        .lineLimit(2)
+                }
+            } else if entry.sort == .worthTheDrive {
+                if let price = station.prices[entry.fuel] {
+                    FuelStore.priceTextAttributed(price, size: 26, weight: .bold, color: .green)
+                }
+                if entry.location == nil {
+                    Text("Best Value unavailable · location needed")
+                        .font(.caption2)
+                        .foregroundStyle(.orange)
+                        .lineLimit(2)
+                } else {
+                    Text("Best Value unavailable · price confidence insufficient")
+                        .font(.caption2)
+                        .foregroundStyle(.orange)
+                        .lineLimit(2)
+                }
             } else if let price = station.prices[entry.fuel] {
                 FuelStore.priceTextAttributed(price, size: 26, weight: .bold, color: .green)
             }
@@ -137,7 +163,9 @@ struct FuelPriceWidgetContent: View {
                     .font(.caption2)
                     .foregroundStyle(.secondary)
                 Spacer()
-                Text(entry.isFavourites ? "cheapest first"
+                Text(entry.sort == .worthTheDrive && entry.bestValuePriceConfidence == .ineligible
+                     ? "price order · Best Value unavailable"
+                     : entry.isFavourites ? "your order"
                      : (entry.locationSource == "none" ? "by price" : "near you"))
                     .font(.caption2)
                     .foregroundStyle(.secondary)