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/Services/IInstanceLocator.cs

@@ -12,6 +12,7 @@ public interface IInstanceLocator
     /// </summary>
     /// <param name="instanceUniqueName">System-wide unique name of the instance to look up.</param>
     /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A task that resolves to the site identifier for the instance, or <c>null</c> if the instance is not found.</returns>
     Task<string?> GetSiteIdForInstanceAsync(
         string instanceUniqueName,
         CancellationToken cancellationToken = default);