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/Models/VoiceSettings.cs

@@ -21,6 +21,11 @@ public sealed class VoiceSettings
     /// <summary>Microphone input gain slider position, 0–300 percent (100 = unity).</summary>
     public int MicGain { get; set; } = 100;
 
+    /// <summary>Send-side mic noise reduction (RNNoise) toggle. MIC stream only, mono only;
+    /// denoises captured mic PCM before input gain and VAD/PTT gate so everyone hears the
+    /// cleaned signal. Independent of the per-listener receive-side NR.</summary>
+    public bool MicNoiseReduction { get; set; } = false;
+
     /// <summary>Push-to-talk key, stored as the integer value of System.Windows.Forms.Keys.</summary>
     public int PttKey { get; set; } = (int)Keys.F8;