Ghostfolio in Japanese

As Ghostfolio continues to evolve, some translations are still missing. We need your help to make Ghostfolio fully accessible to Japanese-speaking users!

Here’s how you can participate in the translation work:

1. Open the translation file at https://github.com/ghostfolio/ghostfolio/blob/main/apps/client/src/locales/messages.ja.xlf
2. Search for entries with state="new"
3. Translate the content of the <target> element
4. Change the state from "new" to "translated"
5. Add the following changelog entry:

## Unreleased

### Changed

- Improved the language localization for Japanese (`ja`)

6. Create a pull request with your translations

You don’t need to translate everything at once. Even small contributions are incredibly valuable and easier for us to review.

Your efforts will make a big difference. Many thanks in advance for your help!