docs: redirect README to CopilotKit monorepo

[onsclom]

What

The skills in this repo have been moved into the main CopilotKit/CopilotKit monorepo under skills/. This rewrites the README as a redirect notice so anyone landing here is pointed at the new source of truth.

Changes

• Adds a prominent "this repository has moved" callout at the top.
• Updates the install command to:

  npx skills add CopilotKit/CopilotKit/skills -y

• Replaces the long-form skill catalog / architecture / pipeline sections (now maintained in the monorepo) with a short "where things are now" table pointing at the monorepo, docs, Discord, and the Agent Skills standard.