feat(i18n): add Korean language support (#367)

* feat(i18n): add Korean language support

- Add Korean (ko) translation files for all namespaces:
  - common.json, auth.json, settings.json, sidebar.json, chat.json, codeEditor.json
- Register Korean locale in config.js and languages.js
- Follow translation guidelines:
  - Keep technical terms in English (UI, API, Shell, Git, etc.)
  - Use Korean phonetic for some terms (TaskMaster → 테스크마스터)
  - Maintain concise translations to match English length where possible

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* fix(i18n): keep technical term "UI" in Korean translation

- Change "인터페이스" back to "UI" in sidebar subtitle
- Keep technical terms in English as per translation guidelines

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

src/i18n/config.js

@@ -21,6 +21,13 @@ import enSidebar from './locales/en/sidebar.json';
 import enChat from './locales/en/chat.json';
 import enCodeEditor from './locales/en/codeEditor.json';
 
+import koCommon from './locales/ko/common.json';
+import koSettings from './locales/ko/settings.json';
+import koAuth from './locales/ko/auth.json';
+import koSidebar from './locales/ko/sidebar.json';
+import koChat from './locales/ko/chat.json';
+import koCodeEditor from './locales/ko/codeEditor.json';
+
 import zhCommon from './locales/zh-CN/common.json';
 import zhSettings from './locales/zh-CN/settings.json';
 import zhAuth from './locales/zh-CN/auth.json';
@@ -60,6 +67,14 @@ i18n
         chat: enChat,
         codeEditor: enCodeEditor,
       },
+      ko: {
+        common: koCommon,
+        settings: koSettings,
+        auth: koAuth,
+        sidebar: koSidebar,
+        chat: koChat,
+        codeEditor: koCodeEditor,
+      },
       'zh-CN': {
         common: zhCommon,
         settings: zhSettings,