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/getting-started/quickstart.md

@@ -239,7 +239,7 @@ Only after the base chat works. Pick what you need:
 hermes gateway setup    # Interactive platform configuration
 ```
 
-Connect [Telegram](/docs/user-guide/messaging/telegram), [Discord](/docs/user-guide/messaging/discord), [Slack](/docs/user-guide/messaging/slack), [WhatsApp](/docs/user-guide/messaging/whatsapp), [Signal](/docs/user-guide/messaging/signal), [Email](/docs/user-guide/messaging/email), or [Home Assistant](/docs/user-guide/messaging/homeassistant), or [Microsoft Teams](/docs/user-guide/messaging/teams).
+Connect [Telegram](/user-guide/messaging/telegram), [Discord](/user-guide/messaging/discord), [Slack](/user-guide/messaging/slack), [WhatsApp](/user-guide/messaging/whatsapp), [Signal](/user-guide/messaging/signal), [Email](/user-guide/messaging/email), or [Home Assistant](/user-guide/messaging/homeassistant), or [Microsoft Teams](/user-guide/messaging/teams).
 
 ### Automation and tools