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

nix/modules/default.nix

@@ -1,26 +0,0 @@
-# The full hyperhive host stack, pulled together in one place — this
-# is what the flake exports as `nixosModules.default` (wrapped with
-# the package/source wiring; see flake.nix). One import covers
-# everything; `services.hyperhive.enable = true` turns the stack on.
-#
-# The forge is mandatory — hive-c0re mirrors every agent's applied
-# config repo into it and it's the canonical store for the meta flake
-# + `internal/*` repos, so there's no enable toggle; it deploys with
-# hyperhive itself. hive-matrix is opt-in (off by default). All
-# subsystems rely on `services.hyperhive.domain`, which is required
-# (asserted in hive-network.nix) whenever hyperhive is enabled.
-{
-  imports = [
-    ./hyperhive.nix
-    ./hive-c0re
-    ./hive-ci.nix
-    ./hive-forge
-    ./hive-gateway
-    ./hive-matrix.nix
-    ./hive-network.nix
-    ./hive-priv.nix
-    ./hive-tls.nix
-    ./otel.nix
-    ./swarm.nix
-  ];
-}