Reserve choice render layer

[han4wluc]

Summary

• Reserve render layer 70 for choices and move top/foreground visuals to layer 80.
• Update visual layer schema/docs/tests so visuals allow 10, 30, 50, and 80; layer 70 is rejected for visuals.
• Update visual layer VT coverage and references to validate choice below top visuals.
• Bump package version to 1.20.1.

Tests

• bun run vitest run spec/renderLayers.test.js spec/projectDataSchema.test.js puty.spec.js
• bun run test
• bun run lint
• git diff --check
• bun run esbuild.js
• rtgl vt screenshot --item visual/layers.yaml --item visual/opacity-blur.yaml --item visual/transform-overrides.yaml --wait-event vt:ready --concurrency 2 --timeout 60000
• rtgl vt report --item visual/layers.yaml --item visual/opacity-blur.yaml --item visual/transform-overrides.yaml