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.SiteEventLogging/ISiteEventLogger.cs

@@ -20,6 +20,7 @@ public interface ISiteEventLogger
     /// Optional free-form detail text (stack traces, compilation errors, etc.).
     /// Stored verbatim — JSON is conventional but not validated or enforced.
     /// </param>
+    /// <returns>A task that completes once the event is durably persisted.</returns>
     Task LogEventAsync(
         string eventType,
         string severity,