Add comprehensive PipeWire audio configuration with noise suppression

- Add modules/sound/pipewire.nix with full PipeWire stack
- Include RNNoise AI-powered noise suppression
- Add EasyEffects with pre-configured presets for mic and speakers
- Include multiple GUI applications (pavucontrol, helvum, qpwgraph, pwvucontrol)
- Add helper scripts: audio-setup, microphone-test, validate-audio
- Optimize for low-latency real-time audio processing
- Enable auto-start and desktop integration
- Remove duplicate PipeWire configs from hardware-co.nix and users/common.nix
- Import sound module through desktop/common.nix for all desktop machines

modules/desktop/common.nix

@@ -3,6 +3,10 @@
   pkgs,
   ...
 }: {
+  imports = [
+    ../sound/pipewire.nix
+  ];
+
   # Common desktop configuration shared across all environments
 
   # XDG Portal configuration for Wayland/X11 compatibility