When any sync action runs and the target project already has a CLAUDE.md,
automatically insert @AGENTS.md / @AGENT_RULES.md import block so
Claude Code picks up the same rules as Codex without manual setup.
- Add sync_claude_md() called at end of sync_agents_template()
- Uses <!-- playbook:claude:start/end --> block markers for idempotent updates
- Skips if no CLAUDE.md exists (Codex users unaffected)
- Skips if @AGENTS.md already present (manual setups respected)
- Add 4 tests covering: no file, append, update block, already-referenced
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>