feat: allow copying events to other days

[edfloreshz]

Description: Users should be able to copy an existing event to another day without having to recreate it manually.

Acceptance Criteria

• User can copy the selected event with ctrl + c.
• Copied event retains all details (title, description, reminders, location, attendees).
• Original event remains unchanged.
• Support copying recurring and non-recurring events.
• Drag-and-drop copy with a modifier key (e.g., Ctrl+drag) could be supported.
• Allow quick duplication to "tomorrow" or "next week" for convenience.

Priority: Medium