Add design system agent skills for common workflows

[Adi-ty]

What?

Closes #77209

This PR adds a set of design system agent skills for common workflows in .agents/skills/, covering:

• component implementation
• adapting designs to code
• design system contribution workflows
• design system code review

Each skill is split into a SKILL.md entry point plus focused reference files, instead of a single monolithic skill.

Why?

Agents working with the WordPress Design System often lack the repo-specific context needed to complete common tasks reliably. This includes workflows like implementing components with @wordpress/ui, translating designs into code, contributing new components or tokens, and reviewing design system changes.

How?

This PR introduces four skills under .agents/skills/:

• design-system-component-implementation
• design-system-figma-to-code
• design-system-contribution
• design-system-code-review

Use of AI Tools

GitHub Copilot was used to help research repository conventions, and refine the skill content, and review the resulting files for accuracy and consistency. All generated content was manually reviewed and edited before submission.

[Adi-ty]

Happy to iterate on the implementation details here based on feedback.

I started with a simple Markdown-based structure in .agents/skills so the skill content itself is easier to review first. Should we consider packaging them so they can be installed via different skill registries? If we’d prefer a different location, packaging model, or installation flow, I’m happy to adjust the implementation in this PR.

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