dsh-locale-ja: Japanese UI Support for DeepSeek Harness

The `dsh-locale-ja` plugin for DSH Harness (DSH) provides Japanese interface support for the Web UI. It includes 1,257 translated strings and offers system font adaptation, persistent language settings, and automatic cleanup upon uninstallation. Once installed via command, users can enable it by selecting Japanese in the settings. Compatible with DSH 0.1.5-rc.2, it is ideal for users who require a Japanese environment.