Create the "Share" functionality for offline event sharing.

### Description:

This ticket focuses on developing the "Share" button functionality within the EventApp. This feature provides a critical fallback mechanism for users who are in areas with no or very poor network connectivity. Instead of attempting to send the event to a relay over a non-existent connection, the app will package the event into a single, portable .zip file. This file can then be shared with another EventApp user via a device's native sharing options (e.g., Bluetooth, WhatsApp, email, Airdrop). The receiving user, who presumably has a stable connection, can then relay the event to the EventServer.