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.NotificationService/ISmtpClientWrapper.cs

@@ -20,6 +20,7 @@ public interface ISmtpClientWrapper
     /// <param name="host">SMTP server hostname or IP address.</param>
     /// <param name="port">SMTP server port.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     Task ConnectAsync(
         string host,
         int port,
@@ -37,6 +38,7 @@ public interface ISmtpClientWrapper
     /// callers that do not authenticate with OAuth2.
     /// </param>
     /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     Task AuthenticateAsync(
         string authType,
         string? credentials,
@@ -48,8 +50,10 @@ public interface ISmtpClientWrapper
     /// <param name="subject">Email subject line.</param>
     /// <param name="body">Plain-text email body.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     Task SendAsync(string from, IEnumerable<string> bccRecipients, string subject, string body, CancellationToken cancellationToken = default);
     /// <summary>Disconnects from the SMTP server gracefully.</summary>
     /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A task that represents the asynchronous operation.</returns>
     Task DisconnectAsync(CancellationToken cancellationToken = default);
 }