Allow duplicating read-only events to a writable calendar

Is your feature request related to a problem? Please describe.

I subscribed to an external read-only calendar, only a few of which events I will attend. When I am planning to attend one, I add an event in my regular calendar, but have to copy over the details manually.

Describe the solution you'd like

A "Duplicate" option in the event edit menu of read-only events, just as for events in editable calendars. Choosing this would either switch the calendar for the duplicate to the default one, or block saving the duplicate until you switch it to a writable calendar.

Describe alternatives you've considered

No response

Additional context

Similar to this (editable event):

Here (read-only event):

Start by inspecting the event edit menu and the existing Duplicate flow for editable events, then trace how read-only events are represented. Done means a read-only event offers duplication, preserves its details, and either targets the default writable calendar or prevents saving until a writable calendar is selected.