feat(app): what's new after an update, drafted by the release tool (ADR 0030, D61)

halkyon_app's WhatsNew reads what each release changed from the app's
assets/whats_new/ (<version>.<language>.txt, English and German, a change
a line): after an update a sheet lists every release since the one the
device showed last, newest first, once; Settings shows the running
version's again, above About. Nothing on a fresh install.

tool/release.dart drafts the missing texts from the commits that count
after "Go on?" (German marked TRANSLATE:), opens them in the editor until
they fit (no mark left, F-Droid's 500 characters) and commits them with
the version. The English is the Forgejo notes' What's new, each language
F-Droid's changelog of the build, written at publishing and copied in by
tool/fdroid_repo.sh. Learn and Train bundle their texts, Learn's 0.22.0
and Train's 0.1.0 written to start.

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/halkyon_train_flutter/pubspec.yaml

@@ -97,6 +97,10 @@ flutter:
     # The instance the build names, unless --dart-define=SERVER_URL=… does
     # (serverpod_flutter's getServerUrl).
     - assets/config.json
+    # What each release changed, one file a release and language
+    # (<version>.<language>.txt), drafted by tool/release.dart and edited
+    # (ADR 0030, D61): halkyon_app's What's new shows them.
+    - assets/whats_new/
     # The app's icon, Lucide's bike (ADR 0031), and Lucide's licence for the
     # licence list (the repository's tool/app_icons.py writes both).
     - assets/icon/halkyon_train_icon.png