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/learn/halkyon_learn_flutter/assets/whats_new/0.22.0.de.txt

@@ -0,0 +1,4 @@
+- Wähle, wie viel ein Assistent nachdenkt, und finde die Assistenten nach Anbieter.
+- Ein Budget für alle deine Assistenten statt eines für jeden.
+- Betreiber vergeben Assistenten an mehrere Personen auf einmal, jede mit einem Budget.
+- Die Rechtschreibprüfung kommt von selbst zurück, eine Minute nachdem LanguageTool nicht antwortete.