Rewrite Introduction and add UI and agentic surfaces page

[Cuervino]

Summary

Rewrites the Introduction page with a revised set of design principles, and adds a new "UI and agentic surfaces" page.

Introduction.mdx

• Replaced the old generic objective section with a revised set of design principles: Affordance, Feedback, Findability, Simplicity, Predictability, Trust and transparency, Observability, Sequential flow
• Updated Consistency (user-centric framing) and Accessibility.
• Removed the old design principles page (content merged here)

AgenticSurfaces.mdx (new page)

• Documents the paradigm shift happening in Q2 2026 as agentic tools enter the mainstream
• Two sections: "The new interaction landscape" (new surfaces, autonomous systems, role of UI) and "Designed for humans and tools" (documented intent, shared body of knowledge)
• Removes designprinciples.mdx

[bert-e]

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[bert-e]

Waiting for approval

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[Cuervino]

/approve

[bert-e]

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[bert-e]

I have successfully merged the changeset of this pull request
into targetted development branches:

• ✔️ development/1.0

Please check the status of the associated issue None.

Goodbye cuervino.