Implementation: improve alert "insufficient item selected"

[RomijnHumanoids]

During the design ticket covering bulk actions #3026 in the task list and corresponding confirmation modals flows and alerts, two small design improvements came up (each has its own small new ticket):

• Improve the current warning message when users want to continue to next step without a selection in report flow.

A screenshot of the current situation:

[RomijnHumanoids]

In this ticket, there is a design improvement with the warning in the alert style that is generally used within openKAT. There's a version of the current flow with a stand alone page for manual objects selection, and a design for the upcoming new report flow with both report type selection and object selection query in one page.

For review: https://www.figma.com/design/EmUOOLqoFVB50syfDjSX9u/%E2%9C%8D%F0%9F%8F%BC-KAT-%7C-For-Review-%7C-Patterns?node-id=2523-1508&t=3nEwmhiLpjBKMpIx-1

[underdarknl]

N.b.

This warning is already generated by Javascript, and needs to be implement in a different way than using the native CustomValidity method (for now) due to the accessibility concerns. Because we already implement using JS, we can rely on JS to also trigger the warning by flipping a class on the error-paragraph.

[NoemiOverdijk]

Apart from a tiny detail in the copy, I think it looks great and I have no further remarks.

[RomijnHumanoids]

Approved for implementation: https://www.figma.com/design/5lYYfE1SqJ9qofjyvwdvtw/%E2%9C%85-KAT-%7C-Approved-%7C-Reports-Flow?node-id=2606-5202&t=IrqZ9F5YP43jeVmR-1