Avoid duplicate bookings!

Problem: The current "double booking" warning is almost invisible. You can only see it if you happen to click exactly on that area. This leads to constant accidental errors.

Proposed solution:

• Active pop-up: As soon as appointments overlap, a window must pop up.

• Confirmation: The user must actively click away the error or confirm it before they can save.

• High-contrast color: The warning must immediately catch the eye (e.g., in red) so that it is not overlooked.