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/screens/plan/plan_screen.dart

@@ -1,15 +1,18 @@
 import 'package:flutter/material.dart';
 
+import '../../widgets/mission_map.dart';
+
 /// Missionsplanung: Karte + Wegpunktliste (Architektur-Doku 3.6/3.7).
-/// Kartenintegration (flutter_map) und Fillet-Geometrie folgen als naechster
-/// Schritt - dies ist bewusst nur der Screen-Platzhalter.
+/// Top-/Bottom-Bar-Overlays (Modus-Umschalter, Draeder, Wegpunktliste) folgen
+/// als naechster Schritt - dies ist bewusst erst die Vollbild-Karte.
 class PlanScreen extends StatelessWidget {
   const PlanScreen({super.key});
 
   @override
   Widget build(BuildContext context) {
     return const Scaffold(
-      body: Center(child: Text('Plan')),
+      extendBodyBehindAppBar: true,
+      body: MissionMap(),
     );
   }
 }