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/locales/ko/codeEditor.json

@@ -0,0 +1,30 @@
+{
+  "toolbar": {
+    "changes": "변경사항",
+    "previousChange": "이전 변경",
+    "nextChange": "다음 변경",
+    "hideDiff": "Diff 하이라이트 숨기기",
+    "showDiff": "Diff 하이라이트 표시",
+    "settings": "에디터 설정",
+    "collapse": "에디터 접기",
+    "expand": "에디터 전체 너비로 펼치기"
+  },
+  "loading": "{{fileName}} 로딩 중...",
+  "header": {
+    "showingChanges": "변경사항 표시"
+  },
+  "actions": {
+    "download": "파일 다운로드",
+    "save": "저장",
+    "saving": "저장 중...",
+    "saved": "저장됨!",
+    "exitFullscreen": "전체화면 종료",
+    "fullscreen": "전체화면",
+    "close": "닫기"
+  },
+  "footer": {
+    "lines": "줄:",
+    "characters": "문자:",
+    "shortcuts": "Ctrl+S로 저장 • Esc로 닫기"
+  }
+}