Add a documentation issue template

[barney-w]

Summary

The repo has issue templates for bugs and feature requests but not for documentation tasks (stories, JSDoc, README improvements, guides).

What to do

1. Create .github/ISSUE_TEMPLATE/documentation.yml following the structure of feature_request.yml
2. Include these fields:
   • Area dropdown: Storybook, JSDoc, README, Guides, Other
   • Description text area for the documentation improvement
   • Contribution checkbox — willing to submit a PR
3. Auto-label the issue with documentation

Useful references

• Existing templates: .github/ISSUE_TEMPLATE/
• Pattern to follow: .github/ISSUE_TEMPLATE/feature_request.yml