Add UI features, alarm ack, historian UTC fix, and Client.UI documentation

Major changes across the client stack:
- Settings persistence (connection, subscriptions, alarm source)
- Deferred OPC UA SDK init for instant startup
- Array/status code formatting, write value popup, alarm acknowledgment
- Severity-colored alarm rows, condition dedup on server side
- DateTimeRangePicker control with preset buttons and UTC text input
- Historian queries use wwTimezone=UTC and OPCQuality column
- Recursive subscribe from tree, multi-select remove
- Connection panel with expander, folder chooser for cert path
- Dynamic tab headers showing subscription/alarm counts
- Client.UI.md documentation with headless-rendered screenshots

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/ZB.MOM.WW.LmxOpcUa.Client.UI.Tests/ZB.MOM.WW.LmxOpcUa.Client.UI.Tests.csproj

@@ -10,6 +10,8 @@
     </PropertyGroup>
 
     <ItemGroup>
+        <PackageReference Include="Avalonia.Headless" Version="11.2.7"/>
+        <PackageReference Include="Avalonia.Themes.Fluent" Version="11.2.7"/>
         <PackageReference Include="xunit.v3" Version="1.1.0"/>
         <PackageReference Include="Shouldly" Version="4.3.0"/>
         <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.12.0"/>