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/ProximityMonitor.swift

@@ -172,4 +172,19 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
 
         lastAlert = "\(brand) · \(String(format: "%.1fp", price)) · \(unit.format(radiusKM)) radius"
     }
+
+    /// Fires a sample local notification shaped exactly like a real price
+    /// alert, for the Settings "test" button. Uses a placeholder station so
+    /// the user can see the alert format without a real entry event. Tapping
+    /// it does what tapping any FuelBoard alert does — opens the app.
+    static func sendTestNotification(fuel: FuelType, radiusKM: Double) {
+        let unit = FuelStore.loadDistanceUnit()
+        let content = UNMutableNotificationContent()
+        content.title = "Cheapest \(fuel.displayName) nearby: Sample Filling Station"
+        content.body = "Sample Filling Station is the cheapest within \(unit.format(radiusKM)) at 132.9p. Tap to open."
+        content.sound = .default
+
+        let request = UNNotificationRequest(identifier: UUID().uuidString, content: content, trigger: nil)
+        UNUserNotificationCenter.current().add(request)
+    }
 }