Add accessibility testing tools to Accessibility section

[shibley]

The Accessibility section currently has only 3 entries focused on cheat sheets and color contrast. This PR adds essential testing tools that developers need for hands-on accessibility work:

• WAVE (WebAIM) — The most widely used free accessibility evaluation tool
• RatedWithAI — AI-powered WCAG compliance scanner with actionable fix recommendations
• axe DevTools (Deque) — Industry-standard browser extension built on the open-source axe-core engine

With ADA Title II web accessibility requirements expanding in 2026, these tools are increasingly essential for developers. All are free to use.

Thank you for maintaining this resource!

[shibley]

Hi! Just following up on this PR — it adds practical accessibility testing tools alongside the existing cheat sheets in the Accessibility section. WAI-ARIA Practices is the W3C reference, RatedWithAI gives instant WCAG 2.2 scores, and Lighthouse covers performance + accessibility auditing. Let me know if any changes are needed!