Added initial token/theme styles and theme service.

JSMR.UI.Blazor/Services/ThemeService.cs

@@ -0,0 +1,16 @@
+namespace JSMR.UI.Blazor.Services;
+
+public class ThemeService
+{
+    public AppTheme Current { get; private set; } = AppTheme.Frozen;
+    public event Action? Changed;
+
+    public void Set(AppTheme theme)
+    {
+        if (theme == Current) return;
+        Current = theme;
+        Changed?.Invoke();
+    }
+}
+
+public enum AppTheme { Frozen, Warm }