Auto-generate CommonMark references for hyperhive's two NixOS module
surfaces via `pkgs.nixosOptionsDoc`:
- `packages.<system>.docs-host` — operator-facing options exposed by
`hyperhive.nixosModules.default` (`services.hive-c0re.*`,
`hyperhive.domain`, `hyperhive.forge.*`, `hyperhive.matrix.*`).
- `packages.<system>.docs-agent` — per-agent options declared in
`nix/templates/harness-base.nix` (model, allowedRecipients,
extraMcpServers, frontend, forge, matrix, gui, …).
- `packages.<system>.docs` — both pages plus a thin `README.md`
index, bundled for publishing.
Declaration links are rewritten to point at the forge source tree
instead of nix-store paths.
Host options come from a stubbed `nixosSystem` eval that force-disables
all hyperhive subsystems — only the *declarations* feed the doc
renderer, no heavy build inputs end up in the closure. Agent options
reuse `nixosConfigurations.agent-base.options` (already evaluated).
Also wired as `checks.<system>.docs` so CI fails fast on eval breakage.
