docs(xmldoc): fill missing XML docs + strip tracking-ID comments across src

Adds <summary>/<param>/<returns>/<inheritdoc> where missing and removes
project bookkeeping IDs (task/tracking refs) from shipped code comments,
so the docs read cleanly and CommentChecker is quiet except for known
false positives (PLC/protocol terms, event/IEqualityComparer inheritdoc).
Doc/comment-only; no logic changed; solution builds clean.

src/Server/ZB.MOM.WW.OtOpcUa.Host/Observability/ObservabilityExtensions.cs

@@ -21,6 +21,7 @@ public static class ObservabilityExtensions
     /// <c>Otlp</c>; <c>OtOpcUa:Telemetry:OtlpEndpoint</c> sets the OTLP endpoint. With no
     /// config the exporter stays Prometheus (the default).
     /// </param>
+    /// <returns>The service collection, for chaining.</returns>
     public static IServiceCollection AddOtOpcUaObservability(this IServiceCollection services, IConfiguration configuration)
     {
         return services.AddZbTelemetry(o =>
@@ -44,6 +45,7 @@ public static class ObservabilityExtensions
     /// <c>MapZbHealth</c>, which also marks its endpoints anonymous.
     /// </summary>
     /// <param name="app">The endpoint route builder.</param>
+    /// <returns>The endpoint route builder, for chaining.</returns>
     public static IEndpointRouteBuilder MapOtOpcUaMetrics(this IEndpointRouteBuilder app)
     {
         app.MapZbMetrics().AllowAnonymous();