Settings: test alert notification button

Fires a local notification shaped exactly like a real price alert (uses the
currently configured alerts fuel + radius), with permission-gated handling:
prompts on first use, guides to Settings when denied. Tapping it opens
FuelBoard, same as a real alert.

FuelBoard/ContentView.swift

@@ -146,6 +146,8 @@ struct ContentView: View {
 
             SettingsView(
                 distanceUnit: $distanceUnit,
+                alertsFuel: alertsFuel,
+                alertsRadiusKM: alertsRadius,
                 onShowOnboarding: { showOnboarding = true }
             )
             .tabItem { Label("Settings", systemImage: "gearshape.fill") }