feat(windows): move audio settings to dedicated dialog, fix device ComboBox accessibility

Audio input settings (device picker, VAD/PTT mode, VAD sensitivity, mic gain,
PTT key) move from the always-visible bottom panel into Settings > Audio...,
matching the macOS/iOS pattern.

The device ComboBox now uses DataSource + DisplayMember="Name" instead of
Items.Add() with no DisplayMember — this fixes both the display bug (was
showing the full DeviceInfo record ToString()) and the NVDA silence on
dropdown open (DataSource binding exposes proper MSAA text per item).

Changes apply live for immediate feedback; Cancel reverts. VoiceSettings
gains InputDeviceId to persist the chosen device across sessions.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

clients/windows/VoiceCat.App/Models/VoiceSettings.cs

@@ -24,6 +24,9 @@ public sealed class VoiceSettings
     /// <summary>Push-to-talk key, stored as the integer value of System.Windows.Forms.Keys.</summary>
     public int PttKey { get; set; } = (int)Keys.F8;
 
+    /// <summary>Saved device ID from the last session; null means use the system default.</summary>
+    public string? InputDeviceId { get; set; } = null;
+
     private static readonly JsonSerializerOptions JsonOptions = new() { WriteIndented = true };
 
     private static string AppDataDir => Path.Combine(