Fix entering single date in date range picker

[Arnei]

When filtering by start date and entering the date by hand, pressing enter after writing only a single date should still result in a filter for that day.
For example, 01/01/2025 results in a range of 01/01/2025 - 01/01/2025. This fixes that.

How to test this

Can be tested as usual. Test if all input methods for the datepicker still work (both mouse and keyboard). Ideally also test other datepickers beside the start date filter, e.g. the one for scheduling events.

[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-1119

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-1119

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/1119/2025-02-25_08-03-04/ .
It might take a few minutes for it to become available.