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/SettingsView.swift

@@ -1,15 +1,22 @@
 import SwiftUI
 import StoreKit
+import UserNotifications
 import WidgetKit
 
-/// Settings tab — distance units, onboarding replay, and a tip jar.
+/// Settings tab — distance units, onboarding replay, a tip jar, and a
+/// test-alert button that previews what a real price notification looks like.
 struct SettingsView: View {
     @Binding var distanceUnit: DistanceUnit
+    /// The fuel + radius currently configured for alerts (mirrors the Alerts
+    /// tab) so the test notification matches what real alerts will say.
+    var alertsFuel: FuelType = .e10
+    var alertsRadiusKM: Double = 3.0
     var onShowOnboarding: () -> Void = {}
 
     @StateObject private var tipStore = TipStore()
     @State private var showTipAlert = false
     @State private var tipAlertMessage = ""
+    @State private var testAlertMessage: String?
 
     var body: some View {
         NavigationStack {
@@ -41,6 +48,23 @@ struct SettingsView: View {
                     Text("Replay the welcome screen, including the location and notification permission prompts.")
                 }
 
+                Section {
+                    Button {
+                        sendTestAlert()
+                    } label: {
+                        Label("Test alert notification", systemImage: "bell.badge.fill")
+                    }
+                    if let testAlertMessage {
+                        Text(testAlertMessage)
+                            .font(.footnote)
+                            .foregroundStyle(.secondary)
+                    }
+                } header: {
+                    Text("Alerts")
+                } footer: {
+                    Text("Sends a notification exactly like a real price alert for \(alertsFuel.displayName.lowercased()) within \(distanceUnit.format(alertsRadiusKM)). Tapping it opens FuelBoard — just like a real alert.")
+                }
+
                 Section {
                     Button {
                         Task { await tipStore.purchase() }
@@ -75,6 +99,32 @@ struct SettingsView: View {
             }
         }
     }
+
+    private func sendTestAlert() {
+        UNUserNotificationCenter.current().getNotificationSettings { settings in
+            Task { @MainActor in
+                switch settings.authorizationStatus {
+                case .authorized, .provisional, .ephemeral:
+                    ProximityMonitor.sendTestNotification(fuel: alertsFuel, radiusKM: alertsRadiusKM)
+                    testAlertMessage = "Test alert sent — check your notification centre."
+                case .denied:
+                    testAlertMessage = "Notifications are turned off for FuelBoard. Enable them in Settings → Notifications → FuelBoard, then try again."
+                default:
+                    // First time — ask, then fire if granted.
+                    UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) { granted, _ in
+                        Task { @MainActor in
+                            if granted {
+                                ProximityMonitor.sendTestNotification(fuel: alertsFuel, radiusKM: alertsRadiusKM)
+                                testAlertMessage = "Test alert sent — check your notification centre."
+                            } else {
+                                testAlertMessage = "Notifications weren't allowed, so no test alert was sent."
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
 }
 
 /// Loads the £4.99 tip product and drives its purchase.