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/cli.md

@@ -157,7 +157,7 @@ quick_commands:
     target: /gateway restart
 ```
 
-Then type `/status`, `/gpu`, or `/restart` in any chat. See the [Configuration guide](/docs/user-guide/configuration#quick-commands) for more examples.
+Then type `/status`, `/gpu`, or `/restart` in any chat. See the [Configuration guide](/user-guide/configuration#quick-commands) for more examples.
 
 ## Preloading Skills at Launch
 
@@ -305,7 +305,7 @@ The CLI shows animated feedback as the agent works:
   ┊ 📄 web_extract (2.1s)
 ```
 
-Cycle through display modes with `/verbose`: `off → new → all → verbose`. This command can also be enabled for messaging platforms — see [configuration](/docs/user-guide/configuration#display-settings).
+Cycle through display modes with `/verbose`: `off → new → all → verbose`. This command can also be enabled for messaging platforms — see [configuration](/user-guide/configuration#display-settings).
 
 ### Tool Preview Length