Settings Debug: device coordinates + in-range station indicator

- Debug section now shows the last device fix (lat/lng to 5dp) and its age.
- In-range indicator uses the SAME criteria as live alerts: stations selling
  the monitored fuel within the alert radius of the fix. Green dot + count
  when in range, red when none, grey while waiting for a fix.
- Shows the cheapest in-range station (name, distance, price).
- ProximityMonitor recomputes the snapshot on every location/stations
  change and on Debug-section appear; ContentView passes the live status.
- SettingsView extracted to its own property to keep TabView body within
  the compiler type-check budget. 35 tests pass.

FuelBoard/ProximityMonitor.swift

@@ -4,6 +4,20 @@ import SwiftUI
 import MapKit
 import UIKit
 
+/// Debug-only location snapshot shown in Settings → Debug. Lets the
+/// developer verify location services while testing: the last fix (with age)
+/// plus how many stations selling the monitored fuel are within the alert
+/// radius of that fix — the exact criteria live alerts use.
+struct DebugLocationStatus: Equatable {
+    var coordinate: Coordinate?
+    var fixAge: TimeInterval?
+    var fuel: FuelType
+    var radiusKM: Double
+    var inRangeCount: Int
+    var cheapestInRange: FuelStation?
+    var cheapestDistanceKM: Double?
+}
+
 /// A station the user wants to see on a map — set when a notification tap
 /// can't hand off to Apple Maps (e.g. inside LiveContainer), so the app shows
 /// an in-app map with directions instead.
@@ -33,6 +47,9 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
     @Published var lastAlert: String?
     @Published private(set) var lastTestResult: String?
     @Published var pendingStationMap: StationMapRequest?
+    /// Debug-only snapshot for the Settings → Debug section. Recomputed on
+    /// every location/stations change via `refreshDebugStatus()`.
+    @Published private(set) var debugStatus: DebugLocationStatus?
 
     private let manager = CLLocationManager()
     private var stations: [FuelStation] = []
@@ -76,6 +93,8 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
         self.fuel = fuel
         self.radiusKM = radiusKM
 
+        refreshDebugStatus()
+
         for region in manager.monitoredRegions {
             manager.stopMonitoring(for: region)
         }
@@ -128,6 +147,33 @@ final class ProximityMonitor: NSObject, ObservableObject, @preconcurrency CLLoca
 
     var isEnabled: Bool { enabled }
 
+    /// Recomputes the Settings → Debug location snapshot from current state.
+    /// "In range" uses the SAME criteria as live alerts: stations selling the
+    /// monitored fuel within the alert radius of the last known location.
+    func refreshDebugStatus() {
+        guard let fix = FuelStore.loadLocationWithDate() else {
+            debugStatus = DebugLocationStatus(
+                coordinate: nil, fixAge: nil,
+                fuel: fuel, radiusKM: radiusKM,
+                inRangeCount: 0, cheapestInRange: nil, cheapestDistanceKM: nil)
+            return
+        }
+        let sellers = stations.filter { $0.prices[fuel] != nil }
+        let inRange = sellers.filter {
+            $0.distanceKM(to: fix.coordinate.lat, lng2: fix.coordinate.lng) <= radiusKM
+        }
+        let cheapest = inRange.min { ($0.prices[fuel] ?? .infinity) < ($1.prices[fuel] ?? .infinity) }
+        let cheapestDistance = cheapest.map {
+            $0.distanceKM(to: fix.coordinate.lat, lng2: fix.coordinate.lng)
+        }
+        debugStatus = DebugLocationStatus(
+            coordinate: fix.coordinate,
+            fixAge: Date().timeIntervalSince(fix.date),
+            fuel: fuel, radiusKM: radiusKM,
+            inRangeCount: inRange.count,
+            cheapestInRange: cheapest, cheapestDistanceKM: cheapestDistance)
+    }
+
     private func requestPermissions() {
         // Region monitoring needs Always location for background delivery.
         switch manager.authorizationStatus {