docs: enhance hub contributing documentation with comprehensive guidelines

- Add communication channels section (Discord, Discourse, GitHub)
- Expand testing section with accurate cscli hubtest workflow
- Add YAML best practices with real-world anchor examples
- Include AI-assisted generation guidelines with disclosure requirements
- Align PR checklist with enforced GitHub PR template
- Add troubleshooting section with common issues and solutions
- Consolidate redundant "Getting Started" and "Getting Involved" sections
- Fix MDX parsing issues and improve markdown formatting
- Add comprehensive git workflow and branch naming conventions
- Include detailed documentation requirements and examples

Author: LaurenceJJones