Enable audio input device selection on Windows

Add AudioDeviceId property to BaseOptions for Windows, allowing
consumers to select a specific audio capture device (e.g. Bluetooth
headset, USB microphone) by device ID.

Changes:
- Add BaseOptions.windows.cs with AudioDeviceId string property
- Pass AudioDeviceId to MediaCaptureInitializationSettings when
  specified, before initializing MediaCapture

Usage:
  // Enumerate available capture devices
  var selector = MediaDevice.GetAudioCaptureSelector();
  var devices = await DeviceInformation.FindAllAsync(selector);
  var btDevice = devices.FirstOrDefault(d => d.Name.Contains("AirPods"));

  var recorder = audioManager.CreateRecorder(new AudioRecorderOptions
  {
      AudioDeviceId = btDevice?.Id
  });

Companion to #208 (iOS/macCatalyst) and #209 (Android).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: jfversluis

src/Plugin.Maui.Audio/AudioRecorder/AudioRecorder.windows.cs

@@ -49,6 +49,12 @@ public async Task StartAsync(string filePath, AudioRecorderOptions? options = nu
 			{
 				StreamingCaptureMode = StreamingCaptureMode.Audio
 			};
+
+			if (!string.IsNullOrEmpty(audioRecorderOptions.AudioDeviceId))
+			{
+				captureSettings.AudioDeviceId = audioRecorderOptions.AudioDeviceId;
+			}
+
 			await InitMediaCapture(captureSettings);
 		}
 		catch (Exception ex)

src/Plugin.Maui.Audio/BaseOptions.windows.cs

@@ -0,0 +1,16 @@
+namespace Plugin.Maui.Audio;
+
+partial class BaseOptions
+{
+    /// <summary>
+    /// Gets or sets the ID of the preferred audio input device.
+    /// <para>
+    /// Set this to a device ID obtained from
+    /// <c>Windows.Devices.Enumeration.DeviceInformation.FindAllAsync</c> using
+    /// <c>Windows.Media.Devices.MediaDevice.GetAudioCaptureSelector()</c> to record
+    /// from a specific device (e.g. a Bluetooth headset or USB microphone).
+    /// When <see langword="null"/>, the system default input device is used.
+    /// </para>
+    /// </summary>
+    public string? AudioDeviceId { get; set; }
+}