Uncheck 'Select all' header cell on page change

[klaraloreen]

Fixes: #1193.

Adds a state variable to control the value of the "Select all" header cell on page change.

Screenshot before issue (page just changed):

Screenshot after issue (page just changed):

[github-actions]

Hi @klaraloreen
Thank you for contributing to the Opencast Admin UI.
We noticed that you have not yet filed an Individual Contributor License Agreement. Doing that (once) helps us to ensure that Opencast stays free for all. If you make your contribution on behalf of an institution, you might also want to file a Corporate Contributor License Agreement (giving you as individual contributor a bit more security as well). It can take a while for this bot to find out about new filings, so if you just filed one or both of the above do not worry about this message!
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EDIT(@lkiesow ): Klara did submit an ICLA to Apereo. It usually takes a while for Apereo to process the submissions. Meanwhile, please ignore the ICLA test and point reviewers to this comment if anyone asks on further pull requests.

[github-actions]

Use docker or podman to test this pull request locally.

Run test server using develop.opencast.org as backend:

podman run --rm -it -p 127.0.0.1:3000:3000 ghcr.io/opencast/opencast-admin-interface:pr-1196

Specify a different backend like stable.opencast.org:

podman run --rm -it -p 127.0.0.1:3000:3000 -e PROXY_TARGET=https://stable.opencast.org ghcr.io/opencast/opencast-admin-interface:pr-1196

It may take a few seconds for the interface to spin up.
It will then be available at http://127.0.0.1:3000.
For more options you can pass on to the proxy, take a look at the README.md.

[github-actions]

This pull request is deployed at test.admin-interface.opencast.org/1196/2025-05-07_08-00-11/ .
It might take a few minutes for it to become available.

[lkiesow]

Looks good for pagination. But I found another problem:

• The select all checkbox keeps being selected after starting an action (Select all → Action → Start Task → e.g. run „Republish Metadata“)