docs: document *_archive.go versioning convention in CLAUDE.md

Archive files hold superseded handler/helper implementations for historical sync; the live path is whatever the version switch in the matching non-archive file or factory routes to for the current network version.

This was prompted by an audit that traced addGasFeesV127 in helpers_archive.go and mistook it for the live gas-debit path (the live path is addGasFeesV133, dispatched at >= 1.133.0). Spell the convention out in the repository structure and Common Patterns sections so agents and reviewers find the dispatch switch before treating an archived function as current.