Feature Request: Add Simplified Chinese (zh-Hans) Support

Hi,

First of all, thank you for building BookShelves — it's a really clean and well-designed reader.

I'd like to suggest adding Simplified Chinese (zh-Hans) localization support to the app.

Currently, the app interface is English-only, which makes it less accessible for Chinese-speaking users. Given that BookShelves already supports a wide range of ebook formats and is great for managing personal libraries, adding basic i18n support would significantly improve usability.

Suggested Improvements:

• Add Simplified Chinese (zh-Hans) UI localization
• Localize key interface elements such as:
  • Shelves / Collections
  • Reading interface controls
  • Settings and system labels
• Ensure proper handling of Chinese text in sorting and searching

Why this matters:

• There is a large number of Chinese-speaking users who read EPUB/PDF
• Many users manage large personal libraries where clear UI language is important
• It would make BookShelves more competitive with other reading apps that already support multiple languages
• Even partial localization (starting with core UI) would already be very helpful.

Thanks again for your work on this app — looking forward to future updates.