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.InboundAPI/ReturnValueValidator.cs

@@ -28,6 +28,7 @@ public static class ReturnValueValidator
     /// </summary>
     /// <param name="resultJson">The JSON-serialized script return value to validate.</param>
     /// <param name="returnDefinition">JSON-serialized list of <see cref="ReturnFieldDefinition"/> entries, or null/empty to skip validation.</param>
+    /// <returns>A <see cref="ReturnValidationResult"/> indicating success or describing the first validation failure.</returns>
     public static ReturnValidationResult Validate(string? resultJson, string? returnDefinition)
     {
         if (string.IsNullOrWhiteSpace(returnDefinition))
@@ -144,10 +145,12 @@ public sealed class ReturnValidationResult
     public string ErrorMessage { get; private init; } = string.Empty;
 
     /// <summary>Returns a successful validation result.</summary>
+    /// <returns>A <see cref="ReturnValidationResult"/> with <see cref="IsValid"/> set to <c>true</c>.</returns>
     public static ReturnValidationResult Valid() => new() { IsValid = true };
 
     /// <summary>Returns a failed validation result with the specified error message.</summary>
     /// <param name="message">Human-readable description of the validation failure.</param>
+    /// <returns>A <see cref="ReturnValidationResult"/> with <see cref="IsValid"/> set to <c>false</c> and the given error message.</returns>
     public static ReturnValidationResult Invalid(string message) =>
         new() { IsValid = false, ErrorMessage = message };
 }