Wire llmPkgs.herdr into home.packages alongside the other llm-agents tools. herdr is already exported by the existing llm-agents input (packages.herdr, v0.7.3) - no new flake input needed. On macOS it installs the upstream release binary; on Linux it builds from source via the numtide cache already trusted in system.nix. Depends on the llm-agents flake.lock bump (rev 6e9f6664e724) which first ships packages.herdr.