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.DeploymentManager/IFlatteningPipeline.cs

@@ -15,6 +15,7 @@ public interface IFlatteningPipeline
     /// </summary>
     /// <param name="instanceId">Id of the instance to flatten and validate.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A task that resolves to the flattened configuration, revision hash, and validation result; or a failure result if flattening could not complete.</returns>
     Task<Result<FlatteningPipelineResult>> FlattenAndValidateAsync(
         int instanceId,
         CancellationToken cancellationToken = default);