fix(release): a snap built in a clone of its own is packed without --output, into the clone

snapcraft builds in LXD with the project mounted at /root/project and passes --output
on unchanged: naming the clone itself, it took the clone for a file in the folder above,
outside the project, and refused it again. Without --output it packs into the clone
(checked with snapcraft 9.2.1 in Todo's clone), from where the release tool moves it.

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/src/release/app_release.dart

@@ -216,13 +216,12 @@ final class const SnapRelease({
   /// otherwise analyse.
   String projectPath(String home) => '$home/.cache/halkyon-release/snap/$name';
 
-  /// Where `snapcraft pack` writes the snap: the release's folder ([out] in
-  /// [root]) for the root's, its clone for any other, as snapcraft packs
-  /// nowhere outside the project it builds (found releasing Todo 0.1.0, 3 Nov
-  /// 2026); the release tool moves it into the release's folder from there.
-  String packPath({
-    required String home,
-    required String root,
-    required String out,
-  }) => atRoot ? '$root/$out' : projectPath(home);
+  /// The folder `snapcraft pack --output` names: the release's folder ([out]
+  /// in [root]) for the root's; none for any other, which snapcraft then packs
+  /// into its clone, where the release tool takes it from. snapcraft builds in
+  /// LXD with the project mounted elsewhere, and takes an `--output` naming the
+  /// clone itself for a file in the folder above it, outside the project, so
+  /// refuses it (found releasing Todo 0.1.0, 3 Nov 2026).
+  String? packOutput({required String root, required String out}) =>
+      atRoot ? '$root/$out' : null;
 }

tool/src/release/releaser.dart

@@ -454,18 +454,13 @@ final class Releaser({
           'clean',
           snap.part,
         ], workingDirectory: project);
-        final packed = snap.packPath(
-          home: Platform.environment['HOME'] ?? '',
-          root: root.path,
-          out: out,
-        );
+        final output = snap.packOutput(root: root.path, out: out);
         await _run('snapcraft', [
           'pack',
-          '--output',
-          packed,
+          if (output != null) ...['--output', output],
         ], workingDirectory: project);
-        if (!snap.atRoot) {
-          File(p.join(packed, snapFile))
+        if (output == null) {
+          File(p.join(project, snapFile))
             ..copySync(p.join(root.path, out, snapFile))
             ..deleteSync();
         }