docs: add xml comments for Essentials routing

src/PepperDash.Essentials.Core/Routing/ITxRouting.cs

@@ -1,8 +1,18 @@
 namespace PepperDash.Essentials.Core
 {
+    /// <summary>
+    /// Represents a routing device (typically a transmitter or source) that provides numeric feedback for its current route.
+    /// Extends <see cref="IRoutingNumeric"/>.
+    /// </summary>
     public interface ITxRouting : IRoutingNumeric
     {
+        /// <summary>
+        /// Feedback indicating the currently routed video source by its numeric identifier.
+        /// </summary>
         IntFeedback VideoSourceNumericFeedback { get; }
+        /// <summary>
+        /// Feedback indicating the currently routed audio source by its numeric identifier.
+        /// </summary>
         IntFeedback AudioSourceNumericFeedback { get; }
     }
 }