feat: reorganize documentation structure and update agent references (#35)

- Move ROI benchmarks to engineering-agent-learning.md with comprehensive insights
- Create structured engineering-agent-approach.md for methodology guidance
- Add universal AGENTS.md format for broad AI tool compatibility
- Add responsible-ai-code and sync-coordinator agents to .claude/agents/
- Update all documentation references to point to engineering-team-agents repo
- Replace Cursor-specific references with universal AGENTS.md format
- Consolidate all learnings, insights, and implementation lessons in learning doc
- Structure approach doc as practical implementation guide

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: niksacdev