Upgrade design system

[dcousens]

This pull request introduces multiple breaking changes and improvements across Keystone’s core packages. The primary focus of the pull request is the transition to @keystar/ui by removing @keystone-ui/*.

A number of seemingly unrelated breaking changes are included to reduce the burden of back-porting functionality that will then be removed soon thereafter. A few notable out-of-band changes include now supporting null defaults in numeric fields, and moving EndSession to only exist as part of @keystone-6/auth.

[dcousens]

@kennedybaird I think adding a checkbox (or cookie, or) that can easily switch between different field modes will be incredibly helpful in debugging UX

[kennedybaird]

@kennedybaird I think adding a checkbox (or cookie, or) that can easily switch between different field modes will be incredibly helpful in debugging UX

@dcousens - to clarify, you'd like this to expand the current tests/sandbox, or a new project in tests/test-projects?

[dcousens]

tests/sandbox, but I think we can defer to @jossmac to know if that is useful in this pull request, or separately

[gautamsi]

@jossmac I am sure you have noticed my work in #9186
We should move in the direction of SSR friendly design so that any SSR only rendering with NextJs 15 and react 19 should not require major rework in this regards.
They are around the corner and my idea is to move towards App router with maximizing SSR use in admin ui.

[kennedybaird]

tests/sandbox, but I think we can defer to @jossmac to know if that is useful in this pull request, or separately

@jossmac, I'm going to start on this in another branch.

Also, wanted to point you towards #8402 if you haven't seen it - maybe you can factor that into this PR?

[gautamsi]

@jossmac @dcousens Is there any timeline on completion on this?

[dcousens]

@gautamsi I think a significant amount of time is needed for QA and documenting or resolving any regressions, maybe the next step is an alpha RC

[gautamsi]

lets plan to do alpha release soon along with #9186 and kill two birds with one stone. I can prepare my branch with changes from de#date.

[jossmac]

For context @gautamsi, I had a few weeks between client projects which I was able to dedicate to this refactor but that's come to an end. I should hopefully find time here and there for bug fixes etc. however it will be far less focused.

[gautamsi]

@jossmac It is going to be difficult to keep waiting for the community. It seems there is no intention to add major changes to the project, it would be good to open this up for community for governance.

I know as a company Thinkmill may have other priority and even new Keystatic but there are so much to work on here.

I have already started using my own release on npm, it would be good to have direction on this repo to make informed decision.

[dcousens]

@gautamsi #9186 and this going out together, and soon, an an alpha sounds good to me; let's try for next week

[dcousens]

This pull request is pretty big, and we could probably keep working on it for quite a while, but it's time to move to the next phase and put out an RC for wider testing.