Tauri Desktop Application that syncs data of a web service

I need a cross-platform native desktop application (macOS, Windows, Linux) that connects to a web service, synchronizes project data for offline use, and manages it in a custom archive format.

Project Data & File Handling:
- Each project consists of static HTML with Vanilla Javascript to show data stored in JSON files and large amounts of image files
- Each project must be stored in a single file bundle – similar to a .zip, but with a custom extension like .xyz.
- New or updated data should be appended to the existing archive without rebuilding the whole archive.
- When displaying project content in the app’s webview, data must be streamed directly from the archive (no unpacking to temporary folders, no full load into memory).
- The application should be the default app for .xyz files and support drag & drop of .xyz files onto the app icon or window to open them

App Structure & UI Requirements:
- List of all known projects (from web account and additional local files)
- Show name, last sync timestamp, Open button
- Context menu with “Reveal in Finder / Explorer” and "Delete"
- On first “Open” of a project, the user selects the local storage location for this project’s archive.
- Support multiple open projects in separate windows or in tabs of one window
- Native Menu Bar with File → Open, File → New Window, File → New Tab, File → Open Recent,...

Authentication & API Integration:
- Main window should display a “Log in to your account” button if no credentials are stored
- Login via an in-app web popup (OAuth-like flow)
- API returns a key/token → store it securely in the user’s directory together with local paths to existing .xyz files

Technical Expectations:
- Use modern, lightweight technologies (e.g. Tauri, Swift + Rust extensions, or similar – no Electron)
- Create a fully functional MVP, visuals/design are not important
- Clean code with inline documentation/comments
- Add console logging for debugging (events like login, sync, archive read/write, etc.)
- Structure code so I can easily extend it later

Deliverables
- Fully working MVP app for at least mac and windows
- Build/setup instructions (README)
- Code commented and structured in a way that is easy to understand
- Archive read/write and streaming logic implemented
- API auth and project sync working with a dummy API
- Native file association for .xyz files

Optional Future Add-Ons
- Auto-Updating
- Background Sync-Service