[UX] Day selector for appointment slot could be improved

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

Hello there,

Here's how appointment calendar show with Nextcloud 31.0.8 on Firefox 142 :

Intuitively, one might think that days which contains eventual selectable slots are the one standing out with a gray background, but it's not :

These are simply the current week days.

Describe the solution you'd like

With this current ui, user has to test and try many days before finding which one contain actually an available slot.

UX would be dramatically better if days cells with a gray background would be those with one or more available slot.

Describe alternatives you've considered

No response

Additional context

Thanks for the great work! 🤗

Start by locating the appointment calendar's day-selector entry point and the logic that identifies days with available slots. Trace how the current gray background is assigned to current-week days, then update the behavior so it marks only days with one or more selectable slots. Verify the result against the screenshots and in Firefox.