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/android/app/src/main/AndroidManifest.xml

@@ -1,4 +1,7 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android">
+    <!-- Fuer OSM-Kartenkacheln, Wind-/Terrain-APIs und die WiFi/TCP-Verbindung
+         zum Flightcontroller (Doku 4.1) auch im Release-Build noetig. -->
+    <uses-permission android:name="android.permission.INTERNET"/>
     <application
         android:label="dmc_app"
         android:name="${applicationName}"
@@ -8,6 +11,7 @@
             android:exported="true"
             android:launchMode="singleTop"
             android:taskAffinity=""
+            android:screenOrientation="sensorLandscape"
             android:theme="@style/LaunchTheme"
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|smallestScreenSize|locale|layoutDirection|fontScale|screenLayout|density|uiMode"
             android:hardwareAccelerated="true"