Upgrade to Spring Boot 4.x

[yeikel]

Issue submitter TODO list

• I've searched for an already existing issues here
• I'm running a supported version of the application which is listed here and the feature is not present there

Is your proposal related to a problem?

No, but it'll help to stay up to date

Describe the feature you're interested in

https://spring.io/blog/2025/11/20/spring-boot-4-0-0-available-now

Version you're running

f51df4c