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>

test/release/notes_test.dart

@@ -16,6 +16,7 @@ void main() {
     AppRelease app = testApp,
     String? previousTag = 'notes-v0.18.0',
     List<Commit> commits = const [],
+    String? whatsNew,
   }) => releaseNotes(
     app: app,
     version: const Version(0, 19, 0),
@@ -24,8 +25,31 @@ void main() {
     certificate: certificate,
     fdroidFingerprint: fingerprint,
     signer: signer,
+    whatsNew: whatsNew,
   );
 
+  test("with what's new, the notes give it in place of the commits", () {
+    final text = notes(
+      commits: const [Commit(hash: 'a', subject: 'feat: tiles')],
+      whatsNew: '- Tiles on the first start.\n\n- Flags.\n',
+    );
+
+    expect(
+      text,
+      contains(
+        "the project's instance.\n"
+        '\n'
+        "### What's new\n"
+        '\n'
+        '- Tiles on the first start.\n'
+        '- Flags.\n'
+        '\n'
+        '### Installing\n',
+      ),
+    );
+    expect(text, isNot(contains('### Features')));
+  });
+
   test("a release's notes list its features and fixes, oldest first, "
       'without their types and scopes', () {
     final text = notes(