Drop CLAUDE.md; Claude Code reads AGENTS.md directly #56

The maintainer's instruction (2026-10-03, confirmed in this session): current Claude Code supports AGENTS.md, so the one-line CLAUDE.md pointer (@AGENTS.md) goes. Done when CLAUDE.md is deleted, AGENTS.md section 17 no longer describes it, and the release tooling's test and README no longer use it as their example root file; the release-sync test still passes. python-multiplatform did the same in its #97.