Add background transformId support and bump version to 1.0.1

[han4wluc]

Summary

• allow background.transformId in presentation actions
• keep image and video backgrounds centered by default, but let authored transforms override position and anchor defaults
• add schema, system, and dedicated VT coverage for transformed background image and layout cases
• bump the package version from 1.0.0 to 1.0.1

Verification

• bun run lint
• bun run test
• VT_DOCKER_CONCURRENCY=1 bun run vt:docker -- --folder background
• bunx rtgl vt report --diff-threshold 0.8 --folder background