docs: backfill XML documentation across 756 files

Adds <summary>, <param>, <typeparam>, and <inheritdoc/> tags to public
members surfaced by commentchecker — resolves 5,847 of 5,869 issues
(99.6%) across three /fixdocs passes.

src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/PollGroupEngine.cs

@@ -66,6 +66,8 @@ public sealed class PollGroupEngine : IAsyncDisposable
     }
 
     /// <summary>Register a new polled subscription and start its background loop.</summary>
+    /// <param name="fullReferences">The list of tag references to poll.</param>
+    /// <param name="publishingInterval">The desired polling interval; will be clamped to the configured minimum.</param>
     public ISubscriptionHandle Subscribe(IReadOnlyList<string> fullReferences, TimeSpan publishingInterval)
     {
         ArgumentNullException.ThrowIfNull(fullReferences);
@@ -81,6 +83,7 @@ public sealed class PollGroupEngine : IAsyncDisposable
 
     /// <summary>Cancel the background loop for a handle returned by <see cref="Subscribe"/>.</summary>
     /// <returns><c>true</c> when the handle was known to the engine and has been torn down.</returns>
+    /// <param name="handle">The subscription handle to cancel.</param>
     public bool Unsubscribe(ISubscriptionHandle handle)
     {
         if (handle is PollSubscriptionHandle h && _subscriptions.TryRemove(h.Id, out var state))
@@ -235,6 +238,7 @@ public sealed class PollGroupEngine : IAsyncDisposable
         TimeSpan Interval,
         CancellationTokenSource Cts)
     {
+        /// <summary>Gets the cache of last-seen values per tag reference.</summary>
         public ConcurrentDictionary<string, DataValueSnapshot> LastValues { get; }
             = new(StringComparer.OrdinalIgnoreCase);
 
@@ -249,6 +253,7 @@ public sealed class PollGroupEngine : IAsyncDisposable
 
     private sealed record PollSubscriptionHandle(long Id) : ISubscriptionHandle
     {
+        /// <summary>Gets a diagnostic identifier for this subscription.</summary>
         public string DiagnosticId => $"poll-sub-{Id}";
     }
 }