Update docs to new structure

[koppor]

This updates the docs. Uses .sdkmanrc.

Follow-up to #12943

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Before:

Extracts the mise things from #13036 - and updates the general documentation

• Use same JDK version for running gradle and development - different JDK versions are supported by Add -ea workflow (both JDK-ea and JavaFX-ea) #13056
• Remove mise at workflows
• Blocked by: Support winget installation 134130/intellij-mise#234
• Check how this affects us: Add mechanism for different package managers to contribute their installed JVM toolchains gradle/gradle#29508
• Go through complete guide

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Notes on NOT using mise

• Not sure if this is really a good idea
  • see How to configure mise for two Java installations - gradle runtime vs. gradle toolchain jdx/mise#4984.
  • foojay resolver should be updated: Add support for mise locations. gradle/foojay-toolchains#110
  • mise plugin should support winget path: https://plugins.jetbrains.com/plugin/24904-mise
• It might be a good idea as JetBrains itself does not like Gradle 8.14 running in JDK 24: https://youtrack.jetbrains.com/issue/IDEA-371665/IDEA-2025.1-doesnt-understand-that-Gradle-8.14-works-on-Java-24

Mandatory checks

• I own the copyright of the code submitted and I license it under the MIT license
• [.] Change in CHANGELOG.md described in a way that is understandable for the average user (if change is visible to the user)
• [.] Tests created for changes (if applicable)
• [.] Manually tested changed features in running JabRef (always required)
• [.] Screenshots added in PR description (if change is visible to the user)
• [.] Checked developer's documentation: Is the information available and up to date? If not, I outlined it in this pull request.
• [.] Checked documentation: Is the information available and up to date? If not, I created an issue at https://github.com/JabRef/user-documentation/issues or, even better, I submitted a pull request to the documentation repository.

[koppor]

The howto "feels" somewhat bloatet - however, reading IDEA 2025.1 doesn't understand that Gradle 8.14 works on Java 24? it might be necessary to describe how to run gradle on a different JDK than we use for compilation.

[subhramit]

See if this screenshot could be cropped a bit more from the left

[koppor]

Better than nothing 🙈

[subhramit]

also?
Or maybe "allow access for both cases"?

[subhramit]

@Yubo-Cao let us know if you have any comments as well, Yubo.
(In retrospect - for now we are merging at the current state)

[trag-bot]

@trag-bot didn't find any issues in the code! ✅✨

[koppor]

@Yubo-Cao let us know if you have any comments as well, Yubo.

Yeah, sure! -- I went ahead with merging as this improves the state.

BTW: I used a Windows Sandbox made by Custom Sandbox, where I installed git with the following command

choco install git.install -y --params "/GitAndUnixToolsOnPath /WindowsTerminal /WindowsTerminalProfile