Feat: add persisted account theme settings

Backend/internal/bootstrap/service.go

@@ -318,6 +318,14 @@ func (service *Service) GetAdmin(ctx context.Context) (*AdminRecord, error) {
 		return nil, err
 	}
 
+	themePresetID, err := service.loadAdminThemePresetID(ctx, record.DisplayName)
+	if err != nil {
+		return nil, err
+	}
+	if themePresetID != "" {
+		record.ThemePresetID = themePresetID
+	}
+
 	return &record, nil
 }