refactor(desktop): split KDE and PipeWire modules

common/optional/desktop/pipewire.nix

@@ -0,0 +1,16 @@
+{
+  # rtkit is optional but recommended for pipewire
+  security.rtkit.enable = true;
+
+  services = {
+    pulseaudio.enable = false;
+
+    pipewire = {
+      enable = true;
+      alsa.enable = true;
+      alsa.support32Bit = true;
+      pulse.enable = true;
+      wireplumber.enable = true;
+    };
+  };
+}