add theme override customizations

LightlessSync/LightlessConfiguration/UiThemeConfigService.cs

@@ -0,0 +1,14 @@
+using LightlessSync.LightlessConfiguration.Configurations;
+
+namespace LightlessSync.LightlessConfiguration;
+
+public class UiThemeConfigService : ConfigurationServiceBase<UiThemeConfig>
+{
+    public const string ConfigName = "ui-theme.json";
+
+    public UiThemeConfigService(string configDir) : base(configDir)
+    {
+    }
+
+    public override string ConfigurationName => ConfigName;
+}