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>

apps/train/release.dart

@@ -0,0 +1,35 @@
+// How Halkyon Train is released (`dart run tool/release.dart train`): the
+// release tool's configuration of it, registered in tool/src/release/apps.dart.
+import '../../tool/src/release/app_release.dart';
+
+/// Halkyon Train's releases: the APK alone (Train is Android's: Health
+/// Connect, the recorder's foreground service, the Polar Loop), connecting
+/// to train.halkyon.eu, published on code.halkyon.app and in the project's
+/// F-Droid repository beside Learn.
+const trainRelease = AppRelease(
+  id: 'train',
+  name: 'Halkyon Train',
+  applicationId: 'app.halkyon.train',
+  directory: 'apps/train',
+  flutterPackage: 'apps/train/halkyon_train_flutter',
+  artifactName: 'halkyon-train',
+  serverUrl: 'https://train.halkyon.eu/',
+  forgejo: 'https://code.halkyon.app',
+  repository: 'project-halkyon/halkyon',
+  // A PKCS #12 keystore of its own outside the repository (also in the
+  // maintainer's password manager), as Learn's: it is the app's identity, and
+  // lost, installed apps can't be updated.
+  android: AndroidSigning(
+    certificateFile: 'tool/release/train-android-certificate.sha256',
+    keystoreVariable: 'HALKYON_TRAIN_ANDROID_KEYSTORE',
+    defaultKeystore: '.local/share/halkyon-train/android-release.p12',
+    aliasVariable: 'HALKYON_TRAIN_ANDROID_KEY_ALIAS',
+    defaultAlias: 'halkyon-train',
+  ),
+  fdroid: FdroidListing(
+    script: 'tool/fdroid_repo.sh',
+    listing: 'tool/release/fdroid',
+    indexCertificateFile: 'tool/release/fdroid-index-certificate.sha256',
+    repositoryUrl: 'https://halkyon.app/fdroid/repo',
+  ),
+);