feat: create and enable hd-idle module

modules/services/dandelion.nix

@@ -5,5 +5,6 @@
     ++ [ (import ./immich.nix) ]
     ++ [ (import ./nextcloud.nix) ]
     ++ [ (import ./home-assistant.nix) ]
-    ++ [ (import ./smart-monitoring.nix) ];
+    ++ [ (import ./smart-monitoring.nix) ]
+    ++ [ (import ./hd-idle.nix) ];
 }

modules/services/hd-idle.nix

@@ -0,0 +1,21 @@
+{ pkgs, lib, ... }:
+{
+  environment.systemPackages = with pkgs; [
+    hdparm
+  ];
+
+  services.udev.extraRules =
+    let
+      mkRule = as: lib.concatStringsSep ", " as;
+      mkRules = rs: lib.concatStringsSep "\n" rs;
+    in
+    mkRules ([
+      (mkRule [
+        ''ACTION=="add|change"''
+        ''SUBSYSTEM=="block"''
+        ''KERNEL=="sd[a-z]"''
+        ''ATTR{queue/rotational}=="1"''
+        ''RUN+="${pkgs.hdparm}/bin/hdparm -B 90 -S 41 /dev/%k"''
+      ])
+    ]);
+}