docs: add archive notice to the README

[apucacao]

Note

This content was written by AI.

This repository is being archived. The notice tells readers these packages are no longer published from here.

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Note

Overview
Adds a GitHub WARNING callout at the top of README.md stating the repository is archived and that packages are no longer maintained or published from this repo.

No code, packages, or build config change—only reader-facing documentation so people see the archival status before install/contributing instructions.

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[changeset-bot]

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Latest commit: b8555c5

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