fix: remove invalid locale prop from RootProvider (#101)

* feat: add i18n support for 8 languages

Add internationalization infrastructure using Fumadocs i18n with
support for English, French, German, Spanish, Japanese, Russian,
Simplified Chinese, and Traditional Chinese.

- Create i18n config with defineI18n (en, fr, de, es, ja, ru, cn, tw)
- Restructure app routes under [lang] dynamic segment
- Pass i18n config to fumadocs-core source loader
- Update layouts to be locale-aware (RootProvider, DocsLayout, shared)
- Add root redirect from / to /en
- Update LLM and OG routes for locale support
- Add cyrillic font subset for Russian support

* fix: remove invalid locale prop from RootProvider

Author: towneh