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.

tests/Server/ZB.MOM.WW.OtOpcUa.AdminUI.Tests/Uns/TagConfigValidatorTests.cs

@@ -0,0 +1,49 @@
+using Shouldly;
+using ZB.MOM.WW.OtOpcUa.AdminUI.Uns.TagEditors;
+using Xunit;
+
+namespace ZB.MOM.WW.OtOpcUa.AdminUI.Tests.Uns;
+
+public sealed class TagConfigValidatorTests
+{
+    [Fact]
+    public void No_driver_type_is_valid()
+        => TagConfigValidator.Validate(null, "{}").ShouldBeNull();
+
+    [Fact]
+    public void Unmapped_driver_has_no_typed_validator_so_is_valid()
+        => TagConfigValidator.Validate("OpcUaClient", "{}").ShouldBeNull();
+
+    [Fact]
+    public void Modbus_has_no_required_field_so_empty_config_is_valid()
+        => TagConfigValidator.Validate("ModbusTcp", "{}").ShouldBeNull();
+
+    // Drivers whose Validate() requires a field: blank config must return an error string.
+    [Theory]
+    [InlineData("S7")]
+    [InlineData("AbCip")]
+    [InlineData("AbLegacy")]
+    [InlineData("TwinCat")]
+    [InlineData("Focas")]
+    public void Required_field_blank_is_rejected(string driverType)
+    {
+        TagConfigValidator.Validate(driverType, "{}").ShouldNotBeNullOrEmpty();
+        TagConfigValidator.Validate(driverType, null).ShouldNotBeNullOrEmpty();
+    }
+
+    [Fact]
+    public void S7_with_address_is_valid()
+        => TagConfigValidator.Validate("S7", """{"address":"DB1.DBW0"}""").ShouldBeNull();
+
+    [Fact]
+    public void AbCip_with_tag_path_is_valid()
+        => TagConfigValidator.Validate("AbCip", """{"tagPath":"Program:Main.Speed"}""").ShouldBeNull();
+
+    [Fact]
+    public void TwinCat_with_symbol_path_is_valid()
+        => TagConfigValidator.Validate("TwinCat", """{"symbolPath":"MAIN.bStart"}""").ShouldBeNull();
+
+    [Fact]
+    public void Driver_type_lookup_is_case_insensitive()
+        => TagConfigValidator.Validate("s7", "{}").ShouldNotBeNullOrEmpty();
+}