Add internal/assets package that downloads and caches app assets from
Hub API with SHA-256 change detection. Assets resolve from synced cache
first, falling back to baked-in directory. Daily sync schedule +
on-demand POST /api/assets/sync endpoint.
Config: assets.sync_enabled + assets.sync_schedule (default 05:00)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>