fix(multivalue): Wave-2 review fixes (MV-2/MV-4/MV-12)

- MV-2: guard unsupported element type before parse (no misleading re-wrap); add Float round-trip test
- MV-4: carry ElementDataType through the two validation-flatten ResolvedAttribute sites (ManagementActor.HandleValidateTemplate, BundleImporter.BuildFlattenedConfigForValidation) so MV-5 validation sees element type via every entry point
- MV-12: include ElementDataType in TemplateAttribute add/update audit payloads + fix stale docstring

src/ZB.MOM.WW.ScadaBridge.Commons/Types/AttributeValueCodec.cs

@@ -72,6 +72,8 @@ public static class AttributeValueCodec
     private static object? ParseScalar(string? s, DataType t)
     {
         if (s is null) throw new FormatException("List elements may not be null.");
+        if (!IsValidElementType(t))
+            throw new FormatException($"Unsupported list element type '{t}'.");
         var c = CultureInfo.InvariantCulture;
         try
         {

src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementActor.cs

@@ -524,6 +524,7 @@ public class ManagementActor : ReceiveActor
                 CanonicalName = a.Name,
                 Value = a.Value,
                 DataType = a.DataType.ToString(),
+                ElementDataType = a.ElementDataType?.ToString(),
                 IsLocked = a.IsLocked,
                 DataSourceReference = a.DataSourceReference
             }).ToList(),

src/ZB.MOM.WW.ScadaBridge.Transport/Import/BundleImporter.cs

@@ -1083,8 +1083,8 @@ public sealed class BundleImporter : IBundleImporter
     /// enumerates for the "Template overwritten" action.
     /// <para>
     /// Update detection compares every scalar field (Value, DataType,
-    /// IsLocked, Description, DataSourceReference) — no field change → no
-    /// audit row, so an idempotent overwrite produces no noise.
+    /// ElementDataType, IsLocked, Description, DataSourceReference) — no field
+    /// change → no audit row, so an idempotent overwrite produces no noise.
     /// </para>
     /// </summary>
     private async Task SyncTemplateAttributesAsync(
@@ -1146,6 +1146,7 @@ public sealed class BundleImporter : IBundleImporter
                         AttributeName = current.Name,
                         current.Value,
                         current.DataType,
+                        current.ElementDataType,
                         current.IsLocked,
                         current.Description,
                         current.DataSourceReference,
@@ -1176,6 +1177,7 @@ public sealed class BundleImporter : IBundleImporter
                         AttributeName = newAttr.Name,
                         newAttr.Value,
                         newAttr.DataType,
+                        newAttr.ElementDataType,
                         newAttr.IsLocked,
                         newAttr.Description,
                         newAttr.DataSourceReference,
@@ -2304,6 +2306,7 @@ public sealed class BundleImporter : IBundleImporter
                 CanonicalName = a.Name,
                 Value = a.Value,
                 DataType = a.DataType.ToString(),
+                ElementDataType = a.ElementDataType?.ToString(),
                 IsLocked = a.IsLocked,
                 Description = a.Description,
                 DataSourceReference = a.DataSourceReference,

tests/ZB.MOM.WW.ScadaBridge.Commons.Tests/Types/AttributeValueCodecTests.cs

@@ -49,6 +49,14 @@ public class AttributeValueCodecTests
         Assert.Equal("[\"ACME, Inc.\"]",
             AttributeValueCodec.Encode(new List<string> { "ACME, Inc." }));
 
+    [Fact]
+    public void RoundTrip_FloatList()
+    {
+        var json = AttributeValueCodec.Encode(new List<float> { 1.5f, 2.25f, -3.75f });
+        var back = (IList<float>)AttributeValueCodec.Decode(json, DataType.List, DataType.Float)!;
+        Assert.Equal(new[] { 1.5f, 2.25f, -3.75f }, back);
+    }
+
     [Fact]
     public void Encode_DoubleList_IsInvariant()
     {