Correct choice visual layer values

[han4wluc]

Summary

• Correct the semantic render stack: visual behind choice is 70, choice is 80, and foreground/top visuals are 90.
• Add a VISUAL_BEHIND_CHOICE layer and render it after dialogue but before choices.
• Update visual layer schema/docs/tests/VT specs and bump package version to 1.20.2.

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