Align README.ru-RU.md with the English README updates from 72aad2c:
add interactive provider/model setup (Option A), restructure config
options into A/B/C, and add new commands to the reference table.
Add README.ru-RU.md and CONTRIBUTING.ru-RU.md following the existing
localization pattern (zh-CN, ja-JP, ko-KR), and add the Русский link to
the language switcher line in all README and CONTRIBUTING variants.
Also add the previously missing 한국어 link to the CONTRIBUTING.zh-CN.md
and CONTRIBUTING.ja-JP.md switchers.
Closes#100