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/apple/macOS/VoiceCatMac/Windows/SettingsWindowController.swift

@@ -58,6 +58,11 @@ final class SettingsWindowController: NSWindowController, NSWindowDelegate {
     }()
     private let inputGainValueLabel = NSTextField(labelWithString: "100%")
 
+    // Send-side mic noise reduction (RNNoise). MIC-only. Persisted via
+    // MainWindowController.inputNoiseReduction.
+    private let nrCheckbox = NSButton(checkboxWithTitle: "Noise reduction (RNNoise)",
+                                       target: nil, action: nil)
+
     // Aux input stream: a second outgoing stream from another hardware input device (e.g. line-in
     // / aux), captured client-side. Device + volume only — aux is always-on. Persisted via
     // MainWindowController.auxEnabled / auxDeviceUID / auxGain.
@@ -168,6 +173,11 @@ final class SettingsWindowController: NSWindowController, NSWindowDelegate {
         inputGainSlider.setAccessibilityHelp("Boost a quiet microphone. 100% is unity.")
         inputGainValueLabel.setAccessibilityLabel("Microphone volume value")
 
+        nrCheckbox.target = self
+        nrCheckbox.action = #selector(nrChanged)
+        nrCheckbox.setAccessibilityLabel("Microphone noise reduction")
+        nrCheckbox.setAccessibilityHelp("RNNoise denoising of your microphone. Cleans your signal for everyone.")
+
         let inputModeRow = NSStackView(views: [inputModeLabel, inputModeControl])
         inputModeRow.orientation = .horizontal
         inputModeRow.spacing = 8
@@ -249,7 +259,7 @@ final class SettingsWindowController: NSWindowController, NSWindowDelegate {
         volumeRow.orientation = .horizontal
         volumeRow.spacing = 8
 
-        let stack = NSStackView(views: [inputModeRow, vadRow, inputGainRow, pttRow, deviceRow,
+        let stack = NSStackView(views: [inputModeRow, vadRow, inputGainRow, nrCheckbox, pttRow, deviceRow,
                                         levelRow, auxHeader, auxCheckbox, auxDeviceRow, auxGainRow,
                                         notificationsHeader, soundsCheckbox, volumeRow,
                                         speechCheckbox, selfTalkCheckbox, pttSoundCheckbox])
@@ -319,6 +329,7 @@ final class SettingsWindowController: NSWindowController, NSWindowDelegate {
 
         inputGainSlider.doubleValue = Double(mc.inputGain * 100)
         updateInputGainLabel()
+        nrCheckbox.state = mc.inputNoiseReduction ? .on : .off
 
         auxCheckbox.state = mc.auxEnabled ? .on : .off
         auxGainSlider.doubleValue = Double(mc.auxGain * 100)
@@ -371,6 +382,14 @@ final class SettingsWindowController: NSWindowController, NSWindowDelegate {
         }
     }
 
+    @objc private func nrChanged() {
+        let on = nrCheckbox.state == .on
+        mainController?.inputNoiseReduction = on
+        if let mc = mainController, mc.micStreamId != 0 {
+            client.setInputNoiseReduction(on)
+        }
+    }
+
     private func updateInputGainLabel() {
         let pct = Int(inputGainSlider.doubleValue.rounded())
         inputGainValueLabel.stringValue = "\(pct)%"