Add coding-agent token cost analysis

[Yohjisakamoto]

Summary

• Add an empirical analysis of coding-agent token costs to the Generative AI section.
• The article reports matched repository-rewrite runs and links the underlying public 140-run dataset.

Verification

• pre-commit run --files README.md (passed)
• git diff --check (passed)

Disclosure

I am affiliated with Tura, which publishes the linked article and benchmark data.