feat: add hybrid input element plugin

[han4wluc]

Summary

• add a new input element plugin with Pixi-rendered UI and a hidden native text engine for IME, clipboard, and keyboard input
• move pointer caret placement and drag selection into Pixi so the hidden DOM control is invisible and non-clickable
• add input schemas, parser/types/docs, VT coverage, Rettangoli navigation entries, and bump the package version to 1.2.0

Testing

• bunx vitest run
• docker run --rm --user $(id -u):$(id -g) -e RTGL_VT_DEBUG=true -e RTGL_VT_CONCURRENCY=1 -v "$PWD:/workspace" docker.io/han4wluc/rtgl:playwright-v1.57.0-rtgl-v1.0.10 rtgl vt screenshot --wait-event vt:ready --concurrency 1 --item input/add-input.yaml --item input/multiline-input.yaml