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.SiteRuntime/ServiceCollectionExtensions.cs

@@ -18,6 +18,7 @@ public static class ServiceCollectionExtensions
     /// overload with an explicit connection string.
     /// </summary>
     /// <param name="services">The DI service collection to register services into.</param>
+    /// <returns>The same <see cref="IServiceCollection"/> to allow chaining.</returns>
     public static IServiceCollection AddSiteRuntime(this IServiceCollection services)
     {
         // SiteStorageService is registered by the Host using AddSiteRuntime(connectionString)
@@ -30,6 +31,7 @@ public static class ServiceCollectionExtensions
     /// </summary>
     /// <param name="services">The DI service collection to register services into.</param>
     /// <param name="siteDbConnectionString">The SQLite connection string for the site local storage database.</param>
+    /// <returns>The same <see cref="IServiceCollection"/> to allow chaining.</returns>
     public static IServiceCollection AddSiteRuntime(this IServiceCollection services, string siteDbConnectionString)
     {
         services.AddSingleton(sp =>
@@ -66,6 +68,7 @@ public static class ServiceCollectionExtensions
 
     /// <summary>Registers any additional DI services needed by the Site Runtime Akka actors.</summary>
     /// <param name="services">The DI service collection to register services into.</param>
+    /// <returns>The same <see cref="IServiceCollection"/> to allow chaining.</returns>
     public static IServiceCollection AddSiteRuntimeActors(this IServiceCollection services)
     {
         // Actor registration is handled by AkkaHostedService.RegisterSiteActors()