docs: add Korean Kanban documentation

Salvages #21823 by @pochi-gio. Adds Korean (ko) Docusaurus locale and
translates Kanban documentation (kanban.md, kanban-tutorial.md) and the
two related skills (devops-kanban-orchestrator, devops-kanban-worker).

Purely additive — adds ko to the locales list in docusaurus.config.ts
and creates the website/i18n/ko/ tree.

website/docusaurus.config.ts

@@ -24,7 +24,7 @@ const config: Config = {
 
   i18n: {
     defaultLocale: 'en',
-    locales: ['en', 'zh-Hans'],
+    locales: ['en', 'zh-Hans', 'ko'],
     localeConfigs: {
       en: {
         label: 'English',
@@ -33,6 +33,10 @@ const config: Config = {
         label: '简体中文',
         htmlLang: 'zh-Hans',
       },
+      ko: {
+        label: '한국어',
+        htmlLang: 'ko',
+      },
     },
   },