Lock app to landscape fullscreen and add first OSM map

- Lock orientation to landscape (sensorLandscape in the manifest,
  SystemChrome.setPreferredOrientations in main.dart) and enable immersive
  fullscreen, matching the prototype's full-bleed map UI (doc 7.7).
- Add MissionMap widget: flutter_map + standard OSM raster tiles, same
  default center/zoom as the HTML prototype (Amsterdam, zoom 16), OSM
  attribution bottom-left. PlanScreen now renders it full-screen instead of
  the placeholder text.
- Add the release-manifest INTERNET permission (previously only present in
  the debug manifest, which would have silently broken tile loading and any
  future network calls in release builds).
- Update the smoke test to check for the FlutterMap widget instead of the
  removed placeholder text.

Verified with flutter analyze, flutter test, and a real run on the
Pixel_10a emulator (fullscreen landscape confirmed, tiles loading).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/lib/ui/widgets/mission_map.dart

@@ -0,0 +1,43 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_map/flutter_map.dart';
+import 'package:latlong2/latlong.dart';
+import 'package:url_launcher/url_launcher.dart';
+
+/// Vollbild-OSM-Karte, entspricht dem Leaflet-`#map` im HTML-Demonstrator:
+/// randlos, ohne Zoom-Buttons (Pinch-to-Zoom/Pan reicht), Standard-OSM-Tiles.
+class MissionMap extends StatelessWidget {
+  const MissionMap({super.key, this.mapController});
+
+  final MapController? mapController;
+
+  // Default-Zentrum/Zoom uebernommen aus dem HTML-Demonstrator
+  // (Drone Mission Control.html: L.map(...).setView([52.3676, 4.9041], 16)).
+  static const _initialCenter = LatLng(52.3676, 4.9041);
+  static const _initialZoom = 16.0;
+
+  @override
+  Widget build(BuildContext context) {
+    return FlutterMap(
+      mapController: mapController,
+      options: const MapOptions(
+        initialCenter: _initialCenter,
+        initialZoom: _initialZoom,
+        minZoom: 3,
+        maxZoom: 19,
+      ),
+      children: [
+        TileLayer(
+          urlTemplate: 'https://tile.openstreetmap.org/{z}/{x}/{y}.png',
+          userAgentPackageName: 'de.dmc.dmc_app',
+          maxZoom: 19,
+        ),
+        SimpleAttributionWidget(
+          alignment: Alignment.bottomLeft,
+          source: const Text('OpenStreetMap contributors'),
+          onTap: () =>
+              launchUrl(Uri.parse('https://www.openstreetmap.org/copyright')),
+        ),
+      ],
+    );
+  }
+}