Show distance to home as a fourth field in the fly-mode details pill

Adds computeDistanceToHomeM() (mission_stats.dart) alongside the
existing rubber-band-target helper, wired through MissionFooterBar ->
BottomStatsBar the same way flyMissionStatus already is. Only appears
once a home point is known, as the last field after waypoint/distance/
duration.

Generalized HomePointIcon to take an optional strokeColor: the map
marker keeps its dark-fill-plus-white-outline look, while the details
pill uses a plain white fill (strokeColor: null) to match the existing
monochrome flag/ruler/clock icons instead of looking like a dropped-in
map pin.

app/lib/ui/screens/fly/fly_screen.dart

@@ -301,16 +301,21 @@ class _FlyScreenState extends ConsumerState<FlyScreen> {
     // Home der Homepoint) kommt aus computeRubberBandTarget, siehe dortige
     // Doku fuer den RTH-Sonderfall.
     final activeWpIndex = telemetry?.activeWaypointIndex;
+    final homePointLatLng =
+        homePoint == null ? null : LatLng(homePoint.lat, homePoint.lon);
+    final currentPosition = telemetry != null && telemetry.hasFix
+        ? LatLng(telemetry.lat, telemetry.lon)
+        : null;
     List<LatLng>? rubberBand;
-    if (telemetry != null && telemetry.hasFix) {
+    if (currentPosition != null && telemetry != null) {
       final target = computeRubberBandTarget(
         navMode: telemetry.navMode,
         activeWaypointIndex: activeWpIndex,
         waypoints: waypoints,
-        homePoint: homePoint == null ? null : LatLng(homePoint.lat, homePoint.lon),
+        homePoint: homePointLatLng,
       );
       if (target != null) {
-        rubberBand = [LatLng(telemetry.lat, telemetry.lon), target];
+        rubberBand = [currentPosition, target];
       }
     }
 
@@ -322,11 +327,19 @@ class _FlyScreenState extends ConsumerState<FlyScreen> {
     final flyMissionStatus = computeFlyMissionStatus(
       waypoints: waypoints,
       activeWaypointIndex: activeWpIndex,
-      currentLat: telemetry != null && telemetry.hasFix ? telemetry.lat : null,
-      currentLon: telemetry != null && telemetry.hasFix ? telemetry.lon : null,
+      currentLat: currentPosition?.latitude,
+      currentLon: currentPosition?.longitude,
       currentSpeedMs: telemetry?.speedMs,
     );
 
+    // Entfernung zum Homepoint als letztes Element der Details-Pille (Doku:
+    // "zeige die Entfernung zum Home Punkt als letztes element in der
+    // details pille im fly modus an").
+    final distanceToHomeM = computeDistanceToHomeM(
+      currentPosition: currentPosition,
+      homePoint: homePointLatLng,
+    );
+
     // Drohnen-Status fuer die Drohnen-Pille (Doku: "im fly modus zeigt die
     // drone pille den zustand der drohne") - das Aussehen des Fly-Modus darf
     // nicht am Vorhandensein eines Telemetrie-Frames haengen (sonst faellt
@@ -430,6 +443,7 @@ class _FlyScreenState extends ConsumerState<FlyScreen> {
             totalDistanceM: missionStats.distanceM,
             totalDurationSec: missionStats.durationSec,
             flyMissionStatus: flyMissionStatus,
+            distanceToHomeM: distanceToHomeM,
             droneStatus: droneStatus,
             warnings: warnings,
             showWarningsBanner: false,