fix(desktop): use releaseType instead of publishingType in electron-builder publish config

electron-builder 26.8.1 rejects publishingType under the GitHub publisher;
the correct option for selecting draft/prerelease/release is releaseType.
Using publishingType caused schema validation to fail during packaging.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

apps/desktop/electron-builder.yml

@@ -44,8 +44,8 @@ publish:
   repo: multica
   # Align with our CLI release flow which pre-creates a *published* GitHub
   # Release via `gh release create`. The electron-builder default of
-  # `publishingType: draft` conflicts with `existingType=release` and causes
+  # `releaseType: draft` conflicts with `existingType=release` and causes
   # uploads of the DMG/ZIP/blockmaps/latest-mac.yml to be silently skipped,
   # which breaks electron-updater auto-update on installed clients.
-  publishingType: release
+  releaseType: release
 npmRebuild: false