Fixes #1421 and adds disclaimer

[skrawcz]

We need to add it to the README that is linked in the package.

This also adds this to all the other packages in this repo.

Changes

• adds incubator disclaimer to README files.

How I tested this

• locally

Notes

Checklist

• PR has an informative and human-readable title (this will be pulled into the release notes)
• Changes are limited to a single goal (no scope creep)
• Code passed the pre-commit check & code is left cleaner/nicer than when first encountered.
• Any change in functionality is tested
• New functions are documented (with a description, list of inputs, and expected output)
• Placeholder code is flagged / future TODOs are captured in comments
• Project documentation has been updated if adding/changing functionality.

[Copilot]

Pull request overview

This PR adds the Apache Software Foundation incubator disclaimer to README files across the repository, addressing issue #1421. The disclaimer informs users that Apache Hamilton is currently undergoing incubation at the ASF and has not yet been fully endorsed.

• Adds identical incubator disclaimer to four README files
• Disclaimer uses proper markdown blockquote formatting
• Placement is consistent across all affected files (after title, before main content)

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
ui/sdk/README.md	Adds incubator disclaimer to the Hamilton UI SDK README
dev_tools/language_server/README.md	Adds incubator disclaimer to the Hamilton Language Server README
contrib/README.md	Adds incubator disclaimer to the contributions package README
README.md	Adds incubator disclaimer to the main repository README

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[jernejfrank]

lgtm