Add skill - Accessibility checks infrastructure setup

## Summary
In some of our projects, we've set up accessibility check infrastructure to validate the UI's compliance with the WCAG 2.2 AA standard.

It would be beneficial to introduce an agentic skill that makes it easy to set up such infrastructure within a new UI project.

## Proposed Scope (high-level, to be refined)
- The skill should check the existing testing infrastructure (Playwright, Cypress, etc.)
- Based on the findings, it should introduce Playwright + Axe Core
- It should add a sample accessibility check and validate that it passes
- It should document the setup (e.g., how to run the checks, where results/reports are generated) so users can pick it up easily

## Out of Scope
Accessibility test creation - this should be handled as a separate skill, distinct from infrastructure setup