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/guides/pipe-script-output.md

@@ -241,9 +241,9 @@ If you just need to pipe a raw string, reach for `hermes send`.
 
 ## Related
 
-- [Automate Anything with Cron](/docs/guides/automate-with-cron) —
+- [Automate Anything with Cron](/guides/automate-with-cron) —
   scheduled jobs whose output auto-delivers to any platform.
-- [Gateway Internals](/docs/developer-guide/gateway-internals) —
+- [Gateway Internals](/developer-guide/gateway-internals) —
   the delivery router that `hermes send` shares with cron delivery.
-- [Messaging Platform Setup](/docs/user-guide/messaging/) —
+- [Messaging Platform Setup](/user-guide/messaging/) —
   one-time configuration for each platform.