refactor: nix/host-modules + nix/agent-modules layout, update doc paths

nix/docs/default.nix

@@ -33,7 +33,7 @@ let
   hostEval = nixosSystem {
     system = pkgs.stdenv.hostPlatform.system;
     modules = [
-      "${nixSrc}/modules"
+      "${nixSrc}/host-modules"
       (
         { lib, ... }:
         {
@@ -51,7 +51,7 @@ let
   };
 
   # Agent module eval from the content-addressed nixSrc. Relative
-  # imports inside agent.nix (the ./harness module dir) resolve
+  # imports inside agent.nix (the ../agent-modules dir) resolve
   # correctly against the nixSrc directory tree. `hyperhive.packages`
   # stays unset — every option default that references it carries a
   # `defaultText`, so the doc walk never forces the packages.
@@ -155,7 +155,7 @@ let
       `hyperhive.nixosModules.default` to operator host configurations
       (`services.hyperhive.{enable,domain,c0re,forge,matrix,gateway}.*`).
     - [per-agent options](agent.md) — options declared in
-      `nix/templates/harness/`, visible from every `agent.nix`
+      `nix/agent-modules/`, visible from every `agent.nix`
       (`hyperhive.model`, `hyperhive.allowedRecipients`,
       `hyperhive.extraMcpServers`, `hyperhive.frontend.*`,
       `hyperhive.forge.*`, `hyperhive.matrix.*`, `hyperhive.gui.*`).