Feature Request: KOReader Sync (Kosync) Support

First off, thank you for building BookShelves! Finding a modern, native, privacy-first ebook reader and library manager for the Apple ecosystem has been amazing, and the native iCloud sync works seamlessly across iPhone, iPad, and Mac.

I noticed that BookShelves already includes a brilliant built-in Calibre wireless sync server to transfer books to devices running KOReader. Because of that, I wanted to propose the logical next step for cross-device harmony: integrating Kosync (KOReader progress synchronization).

Why Kosync for BookShelves?

• Ultimate E-Ink companion: KOReader is widely considered the gold standard reading software for open and jailbroken e-devices (Kobo, Kindle, Onyx Boox, and Android e-paper tablets). Many avid readers prefer e-ink for long sessions but love managing their library and doing quick reading on their Macs or iPhones.

• Bridges the ecosystem gap: While iCloud sync perfectly handles the Apple ecosystem, adding Kosync would turn BookShelves into the ultimate companion app for the physical e-reader community. It allows a user to put down their Kobo or Kindle and pick up right where they left off on their iPhone or Mac.

• THeir API is lightweight & proven: The Kosync protocol is open, straightforward, and already widely implemented in self-hosted tools like Calibre-Web. It essentially tracks basic parameters (document MD5/hash, progress percentage, and timestamp).

• Nice "Pro" pull factor: The e-reader community on Reddit (r/ereader, r/koreader) is massive and highly passionate. There is a constant, desperate search for an elegant iOS/macOS client that syncs seamlessly with KOReader. Adding this feature would tap directly into an eager user base willing to pay for a premium, unified experience.

Even if it starts as an experimental or opt-in setting where users input their own Kosync server details (or an official KOReader account token), it would completely change the game for cross-platform reading.

Thank you for considering it, and keep up the fantastic work on the app!