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.Communication/Grpc/SiteStreamGrpcClient.cs

@@ -100,6 +100,7 @@ public class SiteStreamGrpcClient : IAsyncDisposable, IDisposable
     /// Creates a test-only instance that has no gRPC channel. Used to test
     /// Unsubscribe and Dispose behavior without needing a real endpoint.
     /// </summary>
+    /// <returns>A <see cref="SiteStreamGrpcClient"/> with no channel or client, for testing only.</returns>
     internal static SiteStreamGrpcClient CreateForTesting() => new();
 
     /// <summary>
@@ -153,6 +154,7 @@ public class SiteStreamGrpcClient : IAsyncDisposable, IDisposable
     /// <param name="onEvent">Callback invoked for each domain event received from the stream.</param>
     /// <param name="onError">Callback invoked when the subscription encounters an error.</param>
     /// <param name="ct">Cancellation token to stop the subscription.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     public virtual async Task SubscribeAsync(
         string correlationId,
         string instanceUniqueName,
@@ -257,6 +259,8 @@ public class SiteStreamGrpcClient : IAsyncDisposable, IDisposable
     };
 
     /// <summary>Parses the wire "kind" string back to <see cref="AlarmKind"/>; defaults to Computed.</summary>
+    /// <param name="kind">The wire "kind" string from the gRPC payload; null or unrecognised defaults to <see cref="AlarmKind.Computed"/>.</param>
+    /// <returns>The parsed <see cref="AlarmKind"/>, or <see cref="AlarmKind.Computed"/> when the value is null or unrecognised.</returns>
     internal static AlarmKind ParseAlarmKind(string? kind) =>
         System.Enum.TryParse<AlarmKind>(kind, ignoreCase: true, out var k) ? k : AlarmKind.Computed;
 
@@ -320,6 +324,7 @@ public class SiteStreamGrpcClient : IAsyncDisposable, IDisposable
     /// <summary>
     /// Asynchronously disposes of the gRPC client and all subscriptions.
     /// </summary>
+    /// <returns>A completed <see cref="ValueTask"/> after all subscriptions and the gRPC channel have been released.</returns>
     public virtual ValueTask DisposeAsync()
     {
         ReleaseResources();