Redesign the station listing and move the Best Value controls

Two columns split by a 1pt hairline: identity on the left at a fixed 52%
share so rows line up when scrolling, price and savings on the right,
leading-aligned on one axis with the price dominant. The favourites star
sits under the station logo, freeing the width the pounds-and-pence price
needs to render in full rather than scaled or truncated.

Badges stay tinted rather than filled — BEST VALUE green, CHEAPEST blue,
none for nearest — and the verdict capsule is one shared view across the
listing, the detail sheet and the compact summary, so wording and colour
cannot drift between them.

Best Value's minimum saving moves from Alerts to Settings, Fuel Savings,
beside the fill size and MPG that produce the saving; the Alerts tab reads
it back instead of offering it twice. Its options are now 50p steps to £5
(was 50p/£1/£2/£5), so £2.50 and £3 are reachable, with a test pinning the
step, the ceiling and the store's string round-trip.

The verdict capsule scales to 0.7 before truncating. Measured on a 393pt
screen its copy is handed ~69pt while "Closest station" needs ~90pt, so the
old 0.8 floor could not reach it and rows showed "Closest stati..." instead.

Verified: Debug build clean, swift test 249/249.

FuelBoard/SettingsView.swift

@@ -20,6 +20,12 @@ struct SettingsView: View {
     @Binding var priceDisplayStyle: PriceDisplayStyle
     @Binding var stationTapAction: StationTapAction
     @Binding var fuelSavingsSettings: FuelSavingsSettings
+    /// The Best Value gate — the net saving that makes a station worth the trip.
+    /// Edited here, with the fill size and MPG that PRODUCE that saving, rather
+    /// than in the Alerts tab: the same figure also decides which station rows
+    /// carry the BEST VALUE badge, so it is a fuel-savings setting first and an
+    /// alert setting second. Stored under the alerts key either way.
+    @Binding var bestValueThresholdGBP: Double
     @Binding var dataRefreshMode: DataRefreshMode
     /// The fuel + radius currently configured for alerts (mirrors the Alerts
     /// tab) so the test notification matches what real alerts will say.
@@ -149,6 +155,20 @@ struct SettingsView: View {
                                step: FuelSavingsCalculator.fillAmountSliderStep(for: fuelSavingsSettings.preferredAmount.unit))
                             .accessibilityLabel("Typical fill-up")
                             .accessibilityValue(fillUpText)
+                        Picker("Minimum saving", selection: $bestValueThresholdGBP) {
+                            ForEach(FuelStore.bestValueAlertThresholdOptionsGBP, id: \.self) { value in
+                                Text(FuelSavingsFormat.money(value)).tag(value)
+                            }
+                        }
+                        // Persisted by ContentView's single
+                        // `.onChange(of: alertsBestValueThresholdGBP)`, which
+                        // also refreshes the alert monitor — so this picker
+                        // needs no handler of its own. The store snaps to the
+                        // nearest option, so the picker and the stored value
+                        // cannot disagree.
+                        Text("A saving worth driving for: the net saving left after the extra travel cost. Stations above it are labelled BEST VALUE in the station list, and Best Value alerts use the same figure.")
+                            .font(.caption)
+                            .foregroundStyle(.secondary)
                         if let settingsUnitChangeNotice {
                             Text(settingsUnitChangeNotice)
                                 .font(.caption2)