build(train): Train is released as Learn is, with a key of its own, beside it in the F-Droid repository (ADR 0030, D58)

apps/train/release.dart configures the release tool for Train's APK on
train.halkyon.eu; its release builds sign with its own key when the tool
hands it over. Its F-Droid listing declares NonFreeDep for Polar's SDK and
NonFreeNet; the repository's script copies each app's icon. The key's
certificate is pinned once the key is made.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

test/release/app_release_test.dart

@@ -3,6 +3,7 @@ import 'dart:io';
 import 'package:test/test.dart';
 
 import '../../apps/learn/release.dart';
+import '../../apps/train/release.dart';
 import '../../tool/src/release/apps.dart';
 import '../../tool/src/release/version.dart';
 import 'fixtures.dart';
@@ -74,4 +75,37 @@ void main() {
       contains('name: ${learnRelease.snap!.name}\n'),
     );
   });
+
+  test("Train's release is registered, sound, names files that exist, and "
+      'has a key of its own', () {
+    expect(releasedApps['train'], same(trainRelease));
+    expect(trainRelease.problems(), isEmpty);
+    for (final path in [
+      trainRelease.pubspec,
+      trainRelease.android.certificateFile,
+      ...trainRelease.releaseFiles,
+    ]) {
+      expect(
+        FileSystemEntity.typeSync(path),
+        isNot(FileSystemEntityType.notFound),
+        reason: path,
+      );
+    }
+    expect(trainRelease.snap, isNull);
+    expect(
+      trainRelease.android.certificateFile,
+      isNot(learnRelease.android.certificateFile),
+    );
+    expect(
+      trainRelease.android.defaultKeystore,
+      isNot(learnRelease.android.defaultKeystore),
+    );
+    expect(
+      File(
+        '${trainRelease.fdroid!.listing}/metadata/'
+        '${trainRelease.applicationId}.yml',
+      ).readAsStringSync(),
+      contains('NonFreeDep'),
+    );
+  });
 }