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/Validators/MxGatewayEndpointConfigValidator.cs

@@ -16,6 +16,7 @@ public static class MxGatewayEndpointConfigValidator
     /// </summary>
     /// <param name="config">The MxGateway endpoint configuration to validate.</param>
     /// <param name="fieldPrefix">Optional prefix prepended to each field name in error entries (e.g., "Primary.").</param>
+    /// <returns>A <see cref="ValidationResult"/> with errors for any invalid fields, or a success result when all fields are valid.</returns>
     public static ValidationResult Validate(MxGatewayEndpointConfig config, string fieldPrefix = "")
     {
         var errors = new List<ValidationEntry>();

src/ZB.MOM.WW.ScadaBridge.Commons/Validators/OpcUaEndpointConfigValidator.cs

@@ -16,6 +16,7 @@ public static class OpcUaEndpointConfigValidator
     /// </summary>
     /// <param name="config">The OPC UA endpoint configuration to validate.</param>
     /// <param name="fieldPrefix">Optional prefix prepended to each field name in error entries (e.g., "Primary.").</param>
+    /// <returns>A <see cref="ValidationResult"/> containing field-level errors, or success if all fields are valid.</returns>
     public static ValidationResult Validate(OpcUaEndpointConfig config, string fieldPrefix = "")
     {
         var errors = new List<ValidationEntry>();