feat(theme): resolve database migration blocker and apply ThemePreference column

src/NexusReader.UI.Shared/Components/Molecules/IntelligenceToolbar.razor

@@ -49,7 +49,7 @@
     protected override void OnInitialized()
     {
         FocusMode.OnFocusModeChanged += HandleUpdate;
-        ThemeService.OnThemeChanged += HandleThemeChangedAsync;
+        ThemeService.OnThemeChanged += HandleThemeChanged;
     }
 
     private async Task HandleClearCache()
@@ -68,11 +68,11 @@
 
     private Task HandleUpdate() => InvokeAsync(StateHasChanged);
 
-    private Task HandleThemeChangedAsync() => InvokeAsync(StateHasChanged);
+    private void HandleThemeChanged(ThemeMode mode) => InvokeAsync(StateHasChanged);
 
     public void Dispose()
     {
         FocusMode.OnFocusModeChanged -= HandleUpdate;
-        ThemeService.OnThemeChanged -= HandleThemeChangedAsync;
+        ThemeService.OnThemeChanged -= HandleThemeChanged;
     }
 }