Research Graphify and add a tool guide

## Summary

Research **Graphify** and add a guide for it to the `docs/tools/` section.

Graphify keeps coming up as a token-saving aid for agentic coding. We should evaluate it and document a clear, balanced reference so colleagues can decide whether to adopt it.

## The guide should cover

- What Graphify is and how it works.
- How to install and use it.
- Whether it actually saves tokens and improves the experience of working with an agent — an honest, evidence-based assessment, not marketing claims.
- Pricing / cost model.
- Trade-offs and limitations.

## Notes

- Back the findings with web research across multiple independent sources.
- Keep it tool-general where possible (the team primarily uses GitHub Copilot CLI).