manatee: Add host manatee

hosts/manatee/modules/boot/default.nix

@@ -0,0 +1,43 @@
+{
+  inputs,
+  lib,
+  config,
+  ...
+}:
+let
+  configurationLimit = config.mod.gc.configurationLimit;
+in
+{
+  imports = [ inputs.nix-gc-env.nixosModules.default ];
+
+  options = {
+    mod.gc = {
+      configurationLimit = lib.mkOption {
+        type = lib.types.int;
+        default = 10;
+        description = "number of configuration generations to keep";
+      };
+    };
+  };
+
+  config = {
+    nix.gc = {
+      automatic = true;
+      dates = "weekly";
+
+      # `delete_generations` added by nix-gc-env
+      delete_generations = "+${builtins.toString configurationLimit}";
+    };
+
+    boot = {
+      loader = {
+        systemd-boot = {
+          enable = true;
+          inherit configurationLimit;
+        };
+
+        efi.canTouchEfiVariables = true;
+      };
+    };
+  };
+}