Show the drone's locked home point on the fly-mode map

Adds MSP_WP (118) support to query the flightcontroller's stored home
point (WP#0 is a special case for this in iNAV's getWaypoint(), per
navigation.c) - the FC reports (0,0,0) rather than an error before one
is set, so parseMspHomePoint() treats that pair as "unset". Rendered
with a small pentagon house icon (design/homepoint-pentagon.svg,
ported to a CustomPainter like the other map icons).

Deliberately not polled continuously: a new home_point_provider.dart
refreshes it only at the three moments the FC's home point can
actually change - connect/reconnect, GPS fix acquired, and arming
(iNAV's default reset_home_type=FIRST_ARM only freezes it at the first
arm; before that it continuously follows the aircraft while disarmed).

Mock's implementation offsets the point 25m from the anchor so it
doesn't sit exactly under the drone marker during UI testing.

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

@@ -21,6 +21,7 @@ import '../../../transport/flight_controller_link.dart';
 import '../../providers/active_drone_profile_provider.dart';
 import '../../providers/current_mission_provider.dart';
 import '../../providers/follow_drone_provider.dart';
+import '../../providers/home_point_provider.dart';
 import '../../providers/map_controller_provider.dart';
 import '../../providers/mission_meta_provider.dart';
 import '../../providers/system_message_log_provider.dart';
@@ -29,6 +30,7 @@ import '../../providers/terrain_provider.dart';
 import '../settings/settings_screen.dart';
 import '../../widgets/drone_marker_icon.dart';
 import '../../widgets/drone_status_messages_panel.dart';
+import '../../widgets/home_point_icon.dart';
 import '../../widgets/mission_footer_bar.dart';
 import '../../widgets/mission_map.dart';
 import '../../widgets/waypoint_list_panel.dart';
@@ -189,6 +191,13 @@ class _FlyScreenState extends ConsumerState<FlyScreen> {
     // gekoppelt). Der Rueckgabewert wird hier nicht gebraucht, nur der
     // Beobachtungs-Seiteneffekt.
     ref.watch(systemMessageAutoLogProvider);
+    // Homepoint-Abfrage bei Verbindungsaufbau/GPS-Fix/Armen (Doku: "den auf
+    // der Drohne gelockten Homepoint abfragen ... an diesen drei Stellen
+    // macht es Sinn") - analog systemMessageAutoLogProvider nur der
+    // Beobachtungs-Seiteneffekt, der eigentliche Wert kommt gleich aus
+    // homePointProvider.
+    ref.watch(homePointAutoRefreshProvider);
+    final homePoint = ref.watch(homePointProvider);
 
     // Solange der ueber den GPS-Knopf in der Kopfleiste (FlyMapControls)
     // aktivierte Folgemodus aktiv ist, jede neue Telemetrie-Position
@@ -343,6 +352,20 @@ class _FlyScreenState extends ConsumerState<FlyScreen> {
       navMode: telemetry?.navMode ?? 0,
     );
 
+    // Homepoint-Marker (Doku: "benutze dieses Icon, um den Homepoint
+    // anzuzeigen") - null solange homePointAutoRefreshProvider noch keinen
+    // der drei Trigger-Momente gesehen hat bzw. der FC (noch) keinen
+    // Homepoint gesetzt hat (siehe MspCommands.getWp/parseMspHomePoint-Doku).
+    final homePointMarker = homePoint == null
+        ? null
+        : Marker(
+            point: LatLng(homePoint.lat, homePoint.lon),
+            width: 32,
+            height: 32,
+            alignment: Alignment.center,
+            child: const HomePointIcon(),
+          );
+
     return Stack(
       children: [
         MissionMap(
@@ -362,6 +385,7 @@ class _FlyScreenState extends ConsumerState<FlyScreen> {
               ),
           ],
           droneMarker: droneMarker,
+          homePointMarker: homePointMarker,
         ),
         // Live-Hoehe/-Geschwindigkeit aus der Telemetrie (HTML-Demonstrator:
         // #altReadout/#spdReadout im Fly-Modus) - anders als dort keine