refactor: rename templates to agent.nix/ruth.nix, sweep stale name refs

nix/templates/manager.nix

@@ -1,14 +0,0 @@
-{ lib, ... }:
-{
-  # Entry-point for the privileged root agent (ruth). Referenced from
-  # `flake.nix` (`nixosConfigurations.ruth`) and the meta-flake's
-  # `applied/ruth/flake.nix`.
-  imports = [ ./harness ];
-
-  # The root/manager bootstraps a fresh hive, so it gets the hyperhive
-  # reference docs made available by default (readable at
-  # `$HIVE_DOCS_DIR/`, added via `claude --add-dir`). `mkDefault` so a
-  # manager's own `agent.nix` can still turn it off. Other agents default
-  # off.
-  hyperhive.docs.enable = lib.mkDefault true;
-}