road distance: trigger at launch + foreground, fall back to saved location

Road-distance routing previously only fired once a fresh GPS fix arrived via
the location hook/onChange. A returning user on a cold launch waited for that
fix, and if onboarding/flag issues kept tracking from starting, distances
stayed straight-line. Now:
- refreshRoadDistancesIfNeeded() uses the last saved location when the live
  fix isn't set yet, so it can run immediately.
- It's called explicitly on launch (already-onboarded branch), on foreground
  activation, and on the existing location paths.

FuelBoard/ContentView.swift

@@ -56,14 +56,16 @@ struct ContentView: View {
 
     /// Kicks off a (throttled) Apple-Maps road-distance recompute for the
     /// stations around the current fix. The app owns routing — the widget and
-    /// Live Activity only read the cached result.
+    /// Live Activity only read the cached result. Falls back to the last saved
+    /// location so it can run before the first fresh GPS fix arrives.
     private func refreshRoadDistancesIfNeeded() {
-        guard let location else { return }
+        let origin = location ?? FuelStore.loadLocation()
+        guard let origin else { return }
         Task {
             await RoadDistanceService.refreshIfNeeded(
                 stations: stations,
-                lat: location.lat,
+                lat: origin.lat,
-                lng: location.lng
+                lng: origin.lng
             )
         }
     }
@@ -332,6 +334,10 @@ struct ContentView: View {
                                fuel: alertsFuel, radiusKM: effectiveAlertsRadiusKM)
                 monitor.setEnabled(alertsEnabled)
                 updateLiveActivity()
+                // Compute road distances early (throttled; falls back to the
+                // last saved location) so distance surfaces are road-matched
+                // as soon as stations are available.
+                refreshRoadDistancesIfNeeded()
                 // Refresh only when the cache is stale (twice-a-day policy).
                 // Skipped under the force-* hooks so the banner stays up.
 #if DEBUG
@@ -377,6 +383,7 @@ struct ContentView: View {
                 monitor.update(stations: stations, favourites: refreshedFavourites,
                                fuel: alertsFuel, radiusKM: effectiveAlertsRadiusKM)
                 updateLiveActivity()
+                refreshRoadDistancesIfNeeded()
                 // No network fetch on foreground — pull-to-refresh is the override.
             } else {
                 locationManager.stopForegroundTracking()