### Steps to reproduce

1. Login as a user with permissions to add relations

2. Go to any work package > Relations tab

3. Click on "+Relation" and then add a "Successor" or "Predecessor" relation

4. Use the bottom arrow in the lag field to create a 0 day lag

5. Save


### What is the buggy behavior?

* No error message on the form

* User can save form

* 500 error is shown


### What is the expected behavior?_:_

1. Begin of the insertionHide the stepper on Firefox

2. This should immediately throw an in-line error on any field that is required, in this case it's the Work package field. (Form validation).

1. On clicking Save.

2. Error text eg. "Please select a work package."

3. Add requried label (\*) to Work package.

4. Leave lag as it is.End of the insertion Begin of the deletion TBD by Parimal/front-end meeting groupEnd of the deletion


### Note

if the user adds a huge value to the lag field (i tested with `1234567890111213`) then the 500 error is shown too

if the work package field is filled, the user can save without error but no lag is added (which is expected)

### Screenshots and other files

<img class="op-uc-image op-uc-image_inline" src="/api/v3/attachments/272395/content">

### Environment information

**OpenProject version**

Core build

[d529b3f9447bc8cdf380482da468efa206f36caf](https://github.com/opf/openproject/commits/d529b3f9447bc8cdf380482da468efa206f36caf)

Product version

[201394be8a279687446002df993b8718ff96e38f](https://github.com/opf/saas-openproject/commits/201394be8a279687446002df993b8718ff96e38f)

Core version

OpenProject 15.3.0

**Browser**

* [ ] Chrome
* [x] Firefox 134.0.1
* [ ] Safari
* [ ] Mobile Safari
* [ ] Other (please specify)

**Operating System**

* [x] Windows 11Pro
* [ ] Mac OS X
* [ ] Mobile iOS
* [ ] Mobile Android
* [ ] Linux (please specify distro)
* [ ] Chrome OS
* [ ] Other (please specify)