Fix mediabunny version mismatch in templates, add test

Templates had mediabunny 1.34.4 while catalog specified 1.35.1.
Add a test to validate-templates to ensure template mediabunny
versions always match the catalog. Also improve the
upgrade-mediabunny skill to prevent this from happening again.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>