Update README (2026-06-22) with latest ABOUT.md, INSTALL.md, CONTRIBUTING.md and badges

Author: ocots

README.md

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 please see the user guide: https://github.com/orgs/control-toolbox/discussions/67
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-The CTBase.jl package is part of the [control-toolbox ecosystem](https://github.com/control-toolbox).
+CTBase.jl is the **foundational layer** of the [control-toolbox ecosystem](https://github.com/control-toolbox): it provides the shared types, exception infrastructure, extensions scaffolding, and development utilities that all other packages in the ecosystem build on.
 
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