chore(release): tool/release.sh goes, and the snap goes to the Store's edge

Build 21 (v0.18.0) was the release tool/release.sh was kept for, the one
going with ADR 0014's breaking deploy; every release since is
`dart run tool/release.dart learn`. The comments that named the script
(the F-Droid script, the certificate pin, the Gradle signing) now name
the Dart tool.

Learn's release uploads the snap to the Snap Store's edge channel last,
where v0.18.0 went by hand; the release refuses to start unless
`snapcraft whoami` shows a login.

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/release.dart

@@ -4,8 +4,7 @@ import '../../tool/src/release/app_release.dart';
 
 /// Halkyon Learn's releases: the APK and the snap, both connecting to
 /// learn.halkyon.eu, the project's instance, published on code.halkyon.app,
-/// in the project's F-Droid repository and, once a channel is set, in the
-/// Snap Store.
+/// in the project's F-Droid repository and in the Snap Store's edge channel.
 const learnRelease = AppRelease(
   id: 'learn',
   name: 'Halkyon Learn',
@@ -32,11 +31,13 @@ const learnRelease = AppRelease(
     indexCertificateFile: 'tool/release/fdroid-index-certificate.sha256',
     repositoryUrl: 'https://halkyon.app/fdroid/repo',
   ),
-  // No Store channel yet: the snap is only attached to the release.
+  // To the Store's edge channel (since 23 Oct 2026, as v0.18.0 went there by
+  // hand): stable once the app leaves its early days.
   snap: SnapRelease(
     name: 'halkyon-learn',
     part: 'halkyon-learn',
     directory: 'snap',
+    storeChannel: 'edge',
   ),
   // Learn's releases up to build 21 were tagged v0.18.0 and so on.
   legacyTagPrefix: 'v',