feat(videocodec): add IsCohost to Participant model

Participant exposed IsHost/IsMyself but no co-host role. Several SDKs
(e.g. the ZRC SDK behind epi-zoom-room) report a distinct cohost; add an
IsCohost flag so codecs can surface the Me/Host/Cohost role the mobile
control UI expects.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/PepperDash.Essentials.Devices.Common/VideoCodec/Interfaces/Participant.cs

@@ -15,6 +15,11 @@ namespace PepperDash.Essentials.Devices.Common.VideoCodec.Interfaces
     /// </summary>
     public bool IsHost { get; set; }
 
+    /// <summary>
+    /// Gets or sets the IsCohost
+    /// </summary>
+    public bool IsCohost { get; set; }
+
     /// <summary>
     /// Gets or sets the IsMyself
     /// </summary>