feat(uns): validate typed TagConfig before save (F-uns-2 / #156)

The per-driver editor models expose Validate() (required-field checks) but the
TagModal never called them, so a blank required field (e.g. S7 address, AbCip
tag path) saved silently and only failed at deploy/connect. Add a
TagConfigValidator registry (DriverType -> model.FromJson(json).Validate(),
parallel to TagConfigEditorMap) and call it in SaveAsync before the service
call — a non-null result sets the modal error and blocks save. Unmapped drivers
(no typed editor) and Modbus (no required field) return null. Editors untouched.

AdminUI.Tests 307/307 (12 new validator tests); build clean.

src/Server/ZB.MOM.WW.OtOpcUa.AdminUI/Components/Shared/Uns/TagModal.razor

@@ -197,6 +197,15 @@
         _error = null;
         try
         {
+            // Client-side per-driver config validation (the typed editor's Validate()), so a blank
+            // required field is caught here rather than silently saving and failing at deploy/connect.
+            var configError = TagConfigValidator.Validate(SelectedDriverType, _form.TagConfig);
+            if (configError is not null)
+            {
+                _error = configError;
+                return;
+            }
+
             var input = new TagInput(
                 _form.TagId,
                 _form.Name,