refactor(osd): move volume bindings to audio

configs/nixos/modules/desktop/utilities/audio.nix

@@ -7,6 +7,15 @@
 }:
 # PipeWire as the desktop audio server.
 let
+  volumeKey = keys: command: {
+    inherit keys;
+    repeating = true;
+    action = {
+      kind = "exec";
+      command = "${lib.getExe' pkgs.swayosd "swayosd-client"} --output-volume ${command}";
+    };
+  };
+
   mediaKey = keys: command: {
     inherit keys;
     locked = true;
@@ -30,6 +39,17 @@ in
     };
 
     registry.keybind.${config.networking.hostName} = {
+      volume-up = volumeKey "XF86AudioRaiseVolume" "raise --max-volume 100";
+      volume-down = volumeKey "XF86AudioLowerVolume" "lower";
+      mute = {
+        keys = "XF86AudioMute";
+        locked = true;
+        action = {
+          kind = "exec";
+          command = "${lib.getExe' pkgs.swayosd "swayosd-client"} --output-volume mute-toggle";
+        };
+      };
+
       media-play = mediaKey "XF86AudioPlay" "play-pause";
       media-next = mediaKey "XF86AudioNext" "next";
       media-previous = mediaKey "XF86AudioPrev" "previous";