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

nix/host-modules/default.nix

@@ -0,0 +1,26 @@
+# 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
+  ];
+}