Export specific event

### Problem

There is a button to delete a specific event, and you can also save changes

However sometimes you schedule an event, and want to save up all info within it, for someone to handily double-click a resulting ICS file and add it to their calendars.

### Proposal

Right of the Delete Event button, add an "Export" button.

Clicking it opens a SaveDialog, which an ICS containing the event is saved to.

double-clicking said ICS should offer users of other calendar clients to add the event with all conserved informations.

### Prior Art (Optional)

_No response_