feat(rtzr): add keyword boosting to streaming STT

[lalq]

Description

Added RTZR keyword boosting support by exposing keywords in the STT interface and passing it to the streaming config. Implemented keyword serialization/validation for WebSocket (keyword or keyword:score, (keyword, score) tuples). Documented usage, limits, and Hangul-only requirement in plugin README.

Changes

rtzrapi.py stt.py README.md

Notes

Keyword boosting is only supported for sommers_ko and requires Hangul-only keywords; non-Korean input errors.