fix(website): cross-locale doc links + drop empty ko locale (#31895)

The locale switcher appeared broken because hardcoded markdown links
(`](/docs/X)`) got double-prefixed by Docusaurus to `/docs/<locale>/docs/X`
(404) in non-English locales, and the MDX hero `<a href>` on the index
page escaped locale routing entirely.

Changes:
- Rewrite 922 `](/docs/X)` -> `](/X)` across 166 docs files (strip trailing
  .md too). Docusaurus prepends locale + baseUrl itself.
- docs/index.md -> index.mdx; hero "Get Started" anchor -> Docusaurus
  <Link> so it stays inside the active locale.
- Drop `ko` locale entirely from docusaurus.config.ts + delete i18n/ko/
  (4 stale auto-translated kanban pages, <2% coverage, misleading).

Verified `npm run build` succeeds for both en and zh-Hans; `build/zh-Hans/
index.html` has no /docs/zh-Hans/docs/... double-prefixed paths.

PR2 will translate the 335 English docs into i18n/zh-Hans/.

website/docs/user-guide/features/personality.md

@@ -256,10 +256,10 @@ At a high level, the prompt stack includes:
 
 ## Related docs
 
-- [Context Files](/docs/user-guide/features/context-files)
-- [Configuration](/docs/user-guide/configuration)
-- [Tips & Best Practices](/docs/guides/tips)
-- [SOUL.md Guide](/docs/guides/use-soul-with-hermes)
+- [Context Files](/user-guide/features/context-files)
+- [Configuration](/user-guide/configuration)
+- [Tips & Best Practices](/guides/tips)
+- [SOUL.md Guide](/guides/use-soul-with-hermes)
 
 ## CLI appearance vs conversational personality