Test alert uses real data: actual cheapest station within radius

The first Settings test button no longer sends a hardcoded placeholder —
it runs the same criteria as a live alert (monitored fuel, alert radius,
current location) against the loaded stations and sends the REAL station
name, brand and price. Result line shown under the button; graceful
message when no stations or no sellers within radius.

FuelBoard/ContentView.swift

@@ -148,6 +148,8 @@ struct ContentView: View {
                 distanceUnit: $distanceUnit,
                 alertsFuel: alertsFuel,
                 alertsRadiusKM: alertsRadius,
+                testAlertResult: monitor.lastTestResult,
+                onTestAlert: { monitor.sendTestNotification() },
                 onShowOnboarding: { showOnboarding = true }
             )
             .tabItem { Label("Settings", systemImage: "gearshape.fill") }