v2 registration: "Reject registration" appears in the place of the 2nd pending registration

[timreyn]

Describe the bug

On mobile Chrome, when accepting multiple pending registrations, when you select the first pending person, a "reject registration" button appears exactly where the second pending person was (observe in the two side by side images that they're at the same height). This means that clicking the first person, then attempting to click on the second person, results in rejecting the first person.

(this is especially bad for a certain Extremely Large competition where it takes a few seconds for the page to render, so there is lag between clicking person1 and person2, making it easy to forget about this)

To Reproduce
Steps to reproduce the behavior:

1. Go to https://www.worldcubeassociation.org/competitions/WC2025/edit/registrations on mobile
2. Click the checkbox next to the first pending person
3. Observe that the "reject registrations" button appears where the second pending person was.

Expected behavior
Don't move around other elements on the page that the user might be about to click on.

One option is to use absolute positioning for the buttons, like on the old registration system, so that they don't move other elements around on the page.

Screenshots

Smartphone (please complete the following information):

• Device: Pixel 7a
• OS: Android 15
• Browser: Chrome
• Version 130.0.6723.103

[FinnIckler]

mh.. we are using the sticky component from semantic react and it's supposed to behave in that exact way using position: fixed like in the old version (just on top instead of on the buttom), But it seems to be broken on mobile. Not sure if this is a mistake on our part or a bug in the Sticky component. I can investigate more tomorrow, but I am thinking it might be the latter...