README and AGENTS.md stop documenting build.cmd, LIBCXX_DIR, the
DLL-plus-launcher design rule and the cmd-over-SSH gotcha. The runner
section also drops Ssh, SshWin and Wsl, which were removed from the
code earlier but still had README entries, and the stale pointer to a
deleted cross-arch test. ci.yaml loses the commented-out Windows build,
staging and upload steps and the comments that counted them.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>