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/vision.md

@@ -201,7 +201,7 @@ When a user attaches an image — from the CLI clipboard, the gateway (Telegram/
 
 You don't configure this — Hermes looks up your current model's capability in the provider metadata and picks the right path automatically. The practical effect: you can switch between vision and non-vision models mid-session and image handling "just works" without changing your workflow. Text-only models get coherent context about the image rather than a broken multimodal payload they'd have to reject.
 
-Which auxiliary model handles the text-description path is configurable under `auxiliary.vision` — see [Auxiliary Models](/docs/user-guide/configuration#auxiliary-models).
+Which auxiliary model handles the text-description path is configurable under `auxiliary.vision` — see [Auxiliary Models](/user-guide/configuration#auxiliary-models).
 
 ### `vision_analyze` has the same dual behavior