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/test/widget_test.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter_bloc/flutter_bloc.dart';
+import 'package:flutter_map/flutter_map.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -7,7 +8,7 @@ import 'package:dmc_app/app_mode/app_mode_cubit.dart';
 import 'package:dmc_app/ui/app_shell.dart';
 
 void main() {
-  testWidgets('AppShell zeigt Plan-Screen im Startzustand', (tester) async {
+  testWidgets('AppShell zeigt die Karte im Plan-Startzustand', (tester) async {
     await tester.pumpWidget(
       ProviderScope(
         child: BlocProvider(
@@ -16,7 +17,10 @@ void main() {
         ),
       ),
     );
+    // Nur ein Frame pumpen statt pumpAndSettle: TileLayer laedt echte
+    // Netzwerk-Kacheln, die in der Testumgebung nie ankommen.
+    await tester.pump();
 
-    expect(find.text('Plan'), findsOneWidget);
+    expect(find.byType(FlutterMap), findsOneWidget);
   });
 }