refactor(#234): extract C# IsStrictNetField SSOT predicate (simplify-review)

Code-simplification review's one finding: EntityGenerator expressed the
strict-net predicate twice (HasStrictNetField lambda + AppendNetConverterAttribute
guard). Extracted a single IsStrictNetField(MetaField) helper, aligning C# with the
Java/Kotlin ports that already factor it this way. Behavior-preserving — same logic,
generated output byte-identical (C# Codegen.Tests 334, no fixture drift).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014xy8powhHYJ6gfFt9Ut8dL

Author: dmealing

server/csharp/MetaObjects.Codegen/Generators/EntityGenerator.cs

@@ -825,21 +825,26 @@ private string ApplyPropertyAttributes(string member, MetaObject owner, MetaFiel
         return member[..idx] + hook + member[idx..];
     }
 
-    // #234 — true iff the entity has a (single, non-array) STRICT field.uri / field.inet — the
-    // fields carrying the generated [JsonConverter] + backing MetaNetValidation. A @lenient uri/inet
-    // is a plain string with no converter, so it does not count.
-    private static bool HasStrictNetField(MetaObject entity) =>
-        entity.Fields().Any(f => !f.ResolvedIsArray()
-            && (f.SubType == FIELD_SUBTYPE_URI || f.SubType == FIELD_SUBTYPE_INET)
-            && !CSharpNaming.IsLenientNet(f));
+    // #234 — true iff FIELD is a (single, non-array) STRICT field.uri / field.inet — the fields
+    // carrying the generated [JsonConverter] + backing MetaNetValidation. A @lenient uri/inet is a
+    // plain string with no converter, so it does not count. Single SSOT predicate for both the
+    // per-entity emit gate and the per-property attribute guard (mirrors the Java/Kotlin ports'
+    // own isStrictNetField).
+    private static bool IsStrictNetField(MetaField field) =>
+        !field.ResolvedIsArray()
+        && (field.SubType == FIELD_SUBTYPE_URI || field.SubType == FIELD_SUBTYPE_INET)
+        && !CSharpNaming.IsLenientNet(field);
+
+    // #234 — true iff the entity has any strict field.uri / field.inet (needs MetaNetValidation).
+    private static bool HasStrictNetField(MetaObject entity) => entity.Fields().Any(IsStrictNetField);
 
     // #234 — append the [JsonConverter(typeof(…))] binding a strict field.uri / field.inet property
     // to the same-namespace generated MetaNetValidation converter. No-op for a @lenient uri/inet
     // (a plain string) or any other field. An @isArray uri/inet (element-wise converter) is a
     // follow-up (no validation-conformance case).
     private static void AppendNetConverterAttribute(StringBuilder sb, MetaField field)
     {
-        if (field.ResolvedIsArray() || CSharpNaming.IsLenientNet(field)) return;
+        if (!IsStrictNetField(field)) return; // strict predicate guarantees a non-array uri/inet
         if (field.SubType == FIELD_SUBTYPE_URI)
             sb.AppendLine("    [JsonConverter(typeof(MetaNetValidation.AbsoluteUriJsonConverter))]");
         else if (field.SubType == FIELD_SUBTYPE_INET)