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/Serialization/OpcUaEndpointConfigSerializer.cs

@@ -118,6 +118,7 @@ public static class OpcUaEndpointConfigSerializer
     /// </list>
     /// </summary>
     /// <param name="json">The stored JSON string to parse; null or blank yields a default typed result.</param>
+    /// <returns>An <see cref="OpcUaConfigParseResult"/> containing the parsed config and the detected parse status.</returns>
     public static OpcUaConfigParseResult Deserialize(string? json)
     {
         if (string.IsNullOrWhiteSpace(json))
@@ -175,6 +176,7 @@ public static class OpcUaEndpointConfigSerializer
     /// used by OpcUaDataConnection so the adapter can keep that interface.
     /// </summary>
     /// <param name="config">The endpoint configuration to flatten.</param>
+    /// <returns>A dictionary mapping connection-parameter key names to their string values.</returns>
     public static IDictionary<string, string> ToFlatDict(OpcUaEndpointConfig config)
     {
         var dict = new Dictionary<string, string>