feat(clients): wire RNNoise mic noise reduction into Windows, macOS, and iOS

Expose the existing send-side vc_set_input_noise_reduction C ABI (MIC-only,
mono, LOCAL — denoises captured mic PCM before input gain and VAD/PTT gate)
as a persisted global toggle in each client's audio settings, applied live
and re-applied on Join Voice. Mirrors the existing mic-gain wiring pattern.

- Shared Swift (VoiceCatCore): add setInputNoiseReduction(_:) wrapper
- Windows: P/Invoke + SetInputNoiseReduction wrapper, MicNoiseReduction in
  VoiceSettings, new checkbox in AudioSettingsForm (layout shifted +28px),
  apply on Join Voice; also fix stale 'planned - currently passthrough'
  label on the receive-side per-user NR checkbox (RNNoise now backs it)
- macOS: inputNoiseReduction state + UserDefaults in MainWindowController,
  NR checkbox + nrChanged action in SettingsWindowController
- iOS: inputNoiseReduction in VoiceState + setter + restore in SessionState,
  NR Toggle in SettingsView Voice section

Aux/screen are out of scope by design (core's NR guards kind == MIC). Apple
builds require a rebuilt VoiceCatCore.xcframework with VOICECAT_HAS_NS.

clients/windows/VoiceCat.App/Forms/MainForm.cs

@@ -650,6 +650,7 @@ public partial class MainForm : Form
                 if (mode == VcInputMode.VoiceActivation)
                     _client.SetVadThreshold(VadThresholdFromSettings());
                 _client.SetInputGain(_voiceSettings.MicGain / 100f);
+                _client.SetInputNoiseReduction(_voiceSettings.MicNoiseReduction);
                 SetVoiceJoinedState(true);
                 AddActivity("Joined voice — microphone active");
                 _feedback.PlaySound(SoundEvent.VoiceOn);