review(Driver.OpcUaClient.Browser): add JsonStringEnumConverter (systemic enum bug)

Cross-module fix from the review sweep. -003 (Medium): the browser's JsonOpts lacked
JsonStringEnumConverter (the factory+probe both carry it), so AdminUI string-enum configs
(AuthType/SecurityPolicy/SecurityMode/TargetNamespaceKind) threw on deserialize. Added the
converter (accepts string AND numeric) + TDD.

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser/OpcUaClientDriverBrowser.cs

@@ -1,4 +1,5 @@
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Logging.Abstractions;
 using Opc.Ua;
@@ -16,10 +17,18 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.OpcUaClient.Browser;
 /// </summary>
 public sealed class OpcUaClientDriverBrowser : IDriverBrowser
 {
+    // Kept identical to OpcUaClientDriverFactoryExtensions.JsonOptions and
+    // OpcUaClientDriverProbe._opts so the browser parses a given DriverConfig JSON
+    // the same way as the factory and the probe. The JsonStringEnumConverter lets
+    // enum-valued knobs (SecurityPolicy / SecurityMode / AuthType / TargetNamespaceKind)
+    // be authored as their string names — the natural form for AdminUI-emitted JSON.
+    // JsonStringEnumConverter also accepts numeric ordinals, so existing numeric configs
+    // continue to work without migration.
     private static readonly JsonSerializerOptions JsonOpts = new()
     {
-        UnmappedMemberHandling = System.Text.Json.Serialization.JsonUnmappedMemberHandling.Skip,
+        UnmappedMemberHandling = JsonUnmappedMemberHandling.Skip,
         PropertyNameCaseInsensitive = true,
+        Converters = { new JsonStringEnumConverter() },
     };
 
     private readonly ILogger<OpcUaClientDriverBrowser> _logger;