Add Chinese version of the documentation

[jiayuasu]

Goal

Provide a Chinese (zh) version of the Apache Sedona documentation site at https://sedona.apache.org so that Chinese-speaking users can read installation, tutorial, and API reference content in their native language.

Approach

The site is built with mkdocs-material. We use the mkdocs-static-i18n plugin in suffix mode: a Chinese page lives next to its English source as file.zh.md. Pages without a .zh.md translation automatically fall back to the English content, so the site stays usable while translation lands incrementally.

The default locale remains English. The Chinese build is served at /zh/. A language switcher is rendered in the header by mkdocs-material once both locales are configured.

Rollout plan

Translation lands as a series of small PRs, one per documentation section, so reviewers can verify accuracy without each PR becoming overwhelming. Top-level navigation labels are translated centrally via nav_translations in mkdocs.yml.

Sub-tasks

• Phase 1 — Scaffolding: Wire mkdocs-static-i18n, add zh locale, translate top-level nav labels, seed index.zh.md — [GH-2867] Wire mkdocs-static-i18n for Chinese documentation #2920 ✅
• Phase 2 — Landing pages: [GH-2867] Translate documentation landing pages to Chinese (Phase 2) #2909
• Phase 3 — Setup / Install: [GH-2867] Translate Setup / Install section to Chinese (Phase 3) #2910
• Phase 4 — Tutorial / Programming Guide: [GH-2867] Translate Tutorial / Programming Guide to Chinese (Phase 4) #2911
• Phase 5 — Community & ASF: [GH-2867] Translate Community & ASF section to Chinese (Phase 5) #2912
• Phase 6 — Stats & Viz API: [GH-2867] Translate Stats & Viz API reference to Chinese (Phase 6) #2913
• Phase 7 — SQL API overview & concepts: [GH-2867] Translate SQL API overview & concepts to Chinese (Phase 7) #2914
• Phase 8 — SQL API Geometry / Geography functions: [GH-2867] Translate SQL API Geometry / Geography functions to Chinese (Phase 8) #2915
• Phase 9 — SQL API Raster functions: [GH-2867] Translate SQL API Raster functions to Chinese (Phase 9) #2916
• Phase 10 — SedonaFlink API: [GH-2867] Translate SedonaFlink API reference to Chinese (Phase 10) #2917
• Phase 11 — SedonaSnow API: [GH-2867] Translate SedonaSnow API reference to Chinese (Phase 11) #2918
• Phase 12 — Blog: [GH-2867] Translate Blog landing & selected posts to Chinese (Phase 12) #2919

Notes

• Untranslated pages keep showing English content thanks to fallback_to_default: true.
• Auto-generated content (R pkgdown site under api/rdocs, Python Sphinx site under api/pydocs, JavaDoc, ScalaDoc) stays English-only — these are produced from source comments, not from Markdown files.
• The homepage hero strings live in docs-overrides/main.html, not in index.md. They will be made locale-aware in Phase 2.