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/cron.md

@@ -384,7 +384,7 @@ cronjob(action="create", schedule="every 5m",
 
 It picks `no_agent=True` automatically when the message content is fully determined by the script (watchdogs, threshold alerts, heartbeats). The same tool also lets the agent pause, resume, edit, and remove jobs — so the whole lifecycle is chat-driven without anyone touching the CLI.
 
-See the [Script-Only Cron Jobs guide](/docs/guides/cron-script-only) for worked examples.
+See the [Script-Only Cron Jobs guide](/guides/cron-script-only) for worked examples.
 
 ## Chaining jobs with `context_from`
 
@@ -446,7 +446,7 @@ Outputs are concatenated in the order listed.
 Cron jobs inherit your configured fallback providers and credential pool rotation. If the primary API key is rate-limited or the provider returns an error, the cron agent can:
 
 - **Fall back to an alternate provider** if you have `fallback_providers` (or the legacy `fallback_model`) configured in `config.yaml`
-- **Rotate to the next credential** in your [credential pool](/docs/user-guide/configuration#credential-pool-strategies) for the same provider
+- **Rotate to the next credential** in your [credential pool](/user-guide/configuration#credential-pool-strategies) for the same provider
 
 This means cron jobs that run at high frequency or during peak hours are more resilient — a single rate-limited key won't fail the entire run.