docs: complete XML doc coverage (returns, summaries, inheritdoc)

Resolve all 622 issues flagged by the enhanced CommentChecker: add missing
<returns> tags (incl. the standard phrasing on non-generic Task methods),
add missing <summary> tags, and replace misused/redundant <inheritdoc/> on
members that override or implement nothing with real documentation.
Documentation-only — no behavior change; solution builds clean.

src/ZB.MOM.WW.ScadaBridge.HealthMonitoring/ServiceCollectionExtensions.cs

@@ -11,6 +11,7 @@ public static class ServiceCollectionExtensions
     /// Call this on site nodes only. For central, call AddCentralHealthAggregation() instead.
     /// </summary>
     /// <param name="services">The DI service collection to register into.</param>
+    /// <returns>The same <paramref name="services"/> instance, for call chaining.</returns>
     public static IServiceCollection AddSiteHealthMonitoring(this IServiceCollection services)
     {
         AddOptionsValidation(services);
@@ -24,6 +25,7 @@ public static class ServiceCollectionExtensions
     /// Does not start the HealthReportSender — call AddSiteHealthMonitoring() on site nodes for that.
     /// </summary>
     /// <param name="services">The DI service collection to register into.</param>
+    /// <returns>The same <paramref name="services"/> instance, for call chaining.</returns>
     public static IServiceCollection AddHealthMonitoring(this IServiceCollection services)
     {
         AddOptionsValidation(services);
@@ -37,6 +39,7 @@ public static class ServiceCollectionExtensions
     /// for the central cluster so it appears on /monitoring/health.
     /// </summary>
     /// <param name="services">The DI service collection to register into.</param>
+    /// <returns>The same <paramref name="services"/> instance, for call chaining.</returns>
     public static IServiceCollection AddCentralHealthAggregation(this IServiceCollection services)
     {
         AddOptionsValidation(services);