localization: Update Japanese and Korean translations; add missing Korean locale files

- Updated Japanese translations in config.json, core.json, prompts.json, and startup.json for improved clarity and accuracy.
- Added new Korean locale files for config.json, core.json, prompts.json, and startup.json to support Korean language users.
- Enhanced Chinese translations in core.json and startup.json to include missing resource not found messages and WebUI related texts.

locales/ko/core.json

@@ -0,0 +1,8 @@
+{
+  "core.not_found": "리소스를 찾을 수 없습니다",
+  "core.operation_failed": "작업 실패: {error}",
+  "core.tasks_cancelled": {
+    "one": "{count}개의 작업이 취소되었습니다",
+    "other": "{count}개의 작업이 취소되었습니다"
+  }
+}