Add ValidateHTML tool with description and keywords

[theodcrx]

Added ValidateHTML to the resources list — a free suite of 12 web validation tools (HTML, CSS, JSON, XML, meta tags, Open Graph, accessibility, robots.txt) with instant quality scores from 0 to 100.

• My changes were made in the resources folder, not in the auto-generated README.md file or db folder
• The resource is highly or exclusively related to programming and development
• My submission is formatted according to the guidelines in the contributing guide
• My submission is ordered alphabetically based on the resource name
• My submission has a useful description
• I have searched the repository for any relevant issues or pull requests

[github-actions]

New resource link: https://validatehtml.com

[github-actions]

🤖 Automated PR Validation

⚠️ Issues Found

The following issues were detected. GitHub Copilot will review this PR and report any additional issues.

Resource Validation Errors

🔤 Alphabetical Order

• a.ts:455: Resource "All SVG Icons" should come before "Azure"
• l.ts:456: Resource "LargeMI" should come before "Luthor"
• n.ts:38: Resource "NAT Checker" should come before "NativeBridge"
• t.ts:556: Resource "TypersWorld" should come before "TypingClub"

📊 Too Many Categories

• s.ts:458: Resource "SlingSite": Has 8 categories (max 3)

---

📋 Request for GitHub Copilot

Review this PR and report any issues you find, including:

• Code quality and style issues
• Additional validation errors not caught by automated checks
• Best practices and improvements

---

📚 Resources:

• Contribution Guidelines
• Valid Categories

GitHub Copilot will review this PR and report any issues found.