OpenClaw is no longer used. Removes flake inputs (nix-openclaw,
openclaw-documents), overlays, home-manager modules, config files,
docs, and related TODO/gitignore entries.
The nix-openclaw package renamed the binary from openclaw-gateway to
openclaw, and the gateway now runs as a subcommand. Also adds CLAUDE.md
and openclaw-todo.md.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>