fix: revert gallery template to 11.6.0 to fix CI CE0463

PR #28 re-extracted the gallery template from Mendix 11.6.4, but the CI
runs mx check with 11.6.3. The widget definition changed between those
versions, causing CE0463 on all Gallery widgets in integration tests.

Revert to the original template that matches the CI's mx check version.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: ako