fix(release): the dry run goes on without snapcraft rather than crashing

Where snapcraft is missing, the release is refused already; asking it for
its login then threw, so the dry run stopped before listing the rest.

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/releaser.dart

@@ -835,7 +835,10 @@ final class Releaser({
       _refuse('No JDK found (java, keytool).');
     }
     _environment['PATH'] = '$jdk:${_environment['PATH'] ?? ''}';
-    if (app.snap?.storeChannel case final channel? when channel.isNotEmpty) {
+    // Asked only where snapcraft is there: without, the release was
+    // refused above, and the dry run goes on to say what else it would.
+    if (app.snap?.storeChannel case final channel?
+        when channel.isNotEmpty && _which('snapcraft') != null) {
       final whoami = await Process.run('snapcraft', ['whoami']);
       if (!RegExp(
         r'^username:\s*\S',