docs: add Simplified Chinese (zh) localization

[Alongjie]

Summary

• Add mkdocs-static-i18n plugin configuration to mkdocs.yaml with full Simplified Chinese language support, including an automatic language switcher button in the header
• Add Simplified Chinese (.zh.md) translations for all 28 documentation pages across Home, Indexing, Prompt Tuning, Query, Configuration, CLI, and Extras sections
• Add .zh.ipynb stubs for the three Notebook pages (Global Search, Local Search, DRIFT Search) so the i18n plugin can serve them under the /zh/ locale — content is identical to the English originals
• Fix HTML <img> relative paths in zh pages to account for the /zh/ URL prefix introduced by the i18n build

Dependency

mkdocs-static-i18n needs to be added to the dev dependencies in pyproject.toml:

"mkdocs-static-i18n~=1.0",

Test plan

• Run mkdocs build — should complete without errors
• Run mkdocs serve and switch to 中文 via the header language button
• Verify all translated pages render correctly with images and diagrams intact
• Verify Notebook pages (Global/Local/DRIFT Search) load under /zh/

🤖 Generated with Claude Code

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