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>

docs/adr/0030-halkyon-train.md

@@ -1535,6 +1535,34 @@ Strava. What was found, 27 Oct:
   title, which, tapped, scrolls back up to the row. The row alone is the scroll view's
   header, nothing pinned, so the tabs' lists need no room kept for it and stay plain
   `ListView`s.
+- **D61 What's new, in every Halkyon app** (the developer's; 30 and 31 Oct): after an
+  update, a sheet lists what changed, once per device, and Settings shows it again
+  (`WhatsNewTile`, in the About card), shared in halkyon_app (`WhatsNew`,
+  `WhatsNewOnUpdate` around the tabs, `WhatsNewScope` around the app). Before it,
+  Forgejo's notes listed the feat/fix subjects, and F-Droid and the Snap Store
+  showed nothing (the Snap Store has no field for it).
+  - **One file a release and language** in the app's `assets/whats_new/`
+    (`<version>.<language>.txt`, English and German, a change a line as `- …`),
+    bundled with the app; over one changelog per language, which the app and the
+    tool would parse by sections and which grows with each release.
+  - **Drafted, then edited**: `tool/release.dart`, after *Go on?*, drafts the
+    missing files from the commits that count (features, then fixes, without types,
+    scopes and closing references; German the same lines marked `TRANSLATE:`) and
+    opens them in `$VISUAL`/`$EDITOR` (or waits for Enter) until each lists a change,
+    has no mark left and fits F-Droid's 500 characters; they go into the release
+    commit with the version (the first release's alone, where the pubspec keeps its
+    version). A run stopped there keeps them for the next, the only untracked files
+    a release starts with. The dry run prints them, or the drafts.
+  - **The same text everywhere**: the English as the Forgejo notes' *What's new*, in
+    place of the commits' list, and each language as F-Droid's changelog of the build
+    (`metadata/<app id>/<locale>/changelogs/<build>.txt`, `en-US` and `de`), written
+    by the tool at publishing and copied in by `tool/fdroid_repo.sh`
+    (`HALKYON_FDROID_METADATA`), so nothing is committed twice.
+  - **Every release since**: someone who skipped updates sees each release's changes
+    since the version the device showed last (`whats_new.json` in the support
+    folder), newest first; over the newest alone. Nothing on a fresh install; a device
+    used before (an instance chosen) is shown the running version's on its first start
+    with this. In the app's language, else English.
 
 ## Consequences