docs: condense implementation comments

clients/windows/VoiceCat.Interop/Structs.cs

@@ -43,8 +43,8 @@ internal struct VcCallbacksNative
 internal struct VcStreamDescNative
 {
     public VcStreamKind Kind;
-    public IntPtr DeviceId; // unused by vc_stream_start today — device selection is a
-                             // separate vc_set_input_device call; always IntPtr.Zero here.
+    // Device selection uses vc_set_input_device; stream start passes null.
+    public IntPtr DeviceId;
     public IntPtr Label;
     // Mirrors vc_stream_desc::external_feed. When 1, the core skips its own WASAPI loopback
     // and the caller feeds PCM via StreamFeedPcm (per-app capture path on Windows).