fix(release): every snap packed without --output, into its project, then moved

snapcraft builds in LXD with the project mounted at /root/project and refuses
any --output naming a folder of this machine: the root's own build/release/
for Learn's snap (found releasing Learn 0.23.0) as the clone itself for Todo's
and Train's (Todo 0.1.0, both 3 Nov 2026). Every snap now packs into its
project and is moved into the release's folder from there, checked with
snapcraft 9.2.1 at the root. A failure after none of several apps was done
now says "none" rather than nothing.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

tool/release.dart

@@ -101,8 +101,8 @@ Future<void> main(List<String> arguments) async {
       stderr.writeln('✗ $failure');
       if (targets.length > 1) {
         stderr.writeln(
-          '  Done before it: ${done.map((t) => t.app).join(', ')}; not '
-          'started: ${targets.skip(done.length + 1).map((t) => t.app).join(', ')}.',
+          '  Done before it: ${done.isEmpty ? 'none' : done.map((t) => t.app).join(', ')}; '
+          'not started: ${targets.skip(done.length + 1).map((t) => t.app).join(', ')}.',
         );
       }
       exit(1);