docs: Remove duplicate documentation files from root directory

- Removed ROADMAP.md, DEVELOPMENT_PLAN.md, CONTRIBUTING.md, PROJECT_STATUS.md from root
- Updated README.md to reference docs/ versions instead
- All planning documentation now only exists in docs/ directory
- Prevents duplication as requested

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot