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.Commons/Interfaces/Repositories/INotificationOutboxRepository.cs

@@ -51,6 +51,7 @@ public interface INotificationOutboxRepository
     /// </summary>
     /// <param name="n">The notification to update.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A task that completes when the notification has been persisted.</returns>
     Task UpdateAsync(Notification n, CancellationToken cancellationToken = default);
 
     /// <summary>