feat(webapp-testing): add ScoutQA skill for AI-powered exploratory testing

[phatpham-katalon]

Summary

• Add new webapp-testing plugin with scoutqa-test skill for AI-powered web application testing
• Enable automated exploratory testing, accessibility audits, and user flow validation using ScoutQA CLI

What's Added

Component	Path
New Plugin	plugins/webapp-testing/
New Skill	plugins/webapp-testing/skills/scoutqa-test/SKILL.md

Why This Matters

ScoutQA fills a gap in the testing category by providing autonomous exploratory testing capabilities that complement existing unit/TDD workflows:

• Proactive QA - Automatically verify web features after implementation
• Accessibility-first - Built-in WCAG compliance auditing
• Parallel execution - Run multiple test scenarios concurrently
• Zero test maintenance - Natural language prompts instead of brittle selectors

Use Cases

• Post-deployment smoke tests
• Accessibility audits (WCAG 2.1 AA)
• E-commerce checkout flow validation
• Form validation edge cases
• Mobile responsiveness checks

Changes

• plugins/webapp-testing/skills/scoutqa-test/SKILL.md (new)
• .claude-plugin/marketplace.json - added webapp-testing plugin
• README.md - updated counts (73 plugins, 130 skills)
• docs/agent-skills.md - added Web Application Testing section

Testing

Skill follows the Agent Skills Specification with proper YAML frontmatter and activation triggers.