Add missing exception documentation to public API surface (#1103)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
Co-authored-by: Stephen Toub <stoub@microsoft.com>

src/ModelContextProtocol.Core/Client/HttpClientTransportOptions.cs

@@ -10,6 +10,8 @@ public sealed class HttpClientTransportOptions
     /// <summary>
     /// Gets or sets the base address of the server for SSE connections.
     /// </summary>
+    /// <exception cref="ArgumentNullException">The value is <see langword="null"/>.</exception>
+    /// <exception cref="ArgumentException">The value is not an absolute URI, or does not use the HTTP or HTTPS scheme.</exception>
     public required Uri Endpoint
     {
         get;