feat(centralui): enable tag picker for MxGateway connections

Generalize the browse-button gate from IsOpcUa to IsBrowsable (OPC UA or
MxGateway, both implement IBrowsableDataConnection site-side). The generalized
NodeBrowserDialog + BrowseNodeCommand path already routes by protocol; non-
browsable protocols return NotBrowsable. Test Bindings stays OPC-UA-only (its
read path is out of this slice's scope).

src/ZB.MOM.WW.ScadaBridge.CentralUI/Components/Pages/Deployment/InstanceConfigure.razor

@@ -118,7 +118,7 @@
                             {
                                 var connId = GetBindingConnectionId(attr.Name);
                                 var canBrowse = connId > 0;
-                                var isOpcUa = IsOpcUa(connId);
+                                var isBrowsable = IsBrowsable(connId);
                                 <tr>
                                     <td class="small">@attr.Name</td>
                                     <td class="small text-muted font-monospace">@attr.DataSourceReference</td>
@@ -140,7 +140,7 @@
                                                placeholder="@(attr.DataSourceReference ?? "(no default)")" />
                                     </td>
                                     <td>
-                                        @if (isOpcUa)
+                                        @if (isBrowsable)
                                         {
                                             <button class="btn btn-sm btn-outline-primary"
                                                     disabled="@(!canBrowse)"
@@ -566,13 +566,19 @@
     private string? GetTemplateDefault(string attrName)
         => _bindingDataSourceAttrs.FirstOrDefault(a => a.Name == attrName)?.DataSourceReference;
 
-    /// <summary>True when the row's selected data connection is OPC UA.</summary>
+    /// <summary>
-    private bool IsOpcUa(int connectionId)
+    /// True when the row's selected data connection supports address-space browsing
-        => connectionId > 0
+    /// (the tag picker). OPC UA and MxGateway both implement
-           && string.Equals(
+    /// <c>IBrowsableDataConnection</c> site-side; other protocols return a
-               _siteConnections.FirstOrDefault(c => c.Id == connectionId)?.Protocol,
+    /// NotBrowsable failure, so the button is hidden for them.
-               "OpcUa",
+    /// </summary>
-               StringComparison.OrdinalIgnoreCase);
+    private bool IsBrowsable(int connectionId)
+    {
+        if (connectionId <= 0) return false;
+        var protocol = _siteConnections.FirstOrDefault(c => c.Id == connectionId)?.Protocol;
+        return string.Equals(protocol, "OpcUa", StringComparison.OrdinalIgnoreCase)
+            || string.Equals(protocol, "MxGateway", StringComparison.OrdinalIgnoreCase);
+    }
 
     /// <summary>
     /// Opens the OPC UA tag browser dialog for the given attribute row. Remembers