feat: upgrade to Angular 16.1

frontend/app/src/theme/colors.scss

@@ -12,7 +12,7 @@
  * You should have received a copy of the GNU General Public License along with
  * this program. If not, see <https://www.gnu.org/licenses/>.
  */
-@import 'util/color-system';
+@import './util/color-system';
 
 @include ion-color(primary, #3880ff);
 @include ion-color(secondary, #32db64);

frontend/app/src/theme/common/_ion-header.scss

@@ -1,4 +1,6 @@
 app-root ion-header[class*='header-'] {
+  box-shadow: unset;
+
   &::after {
     background-image: unset;
   }

frontend/app/src/theme/variables.scss

@@ -16,8 +16,6 @@
 // http://ionicframework.com/docs/theming/
 @import './colors';
 
-@import '~swiper/css/navigation';
-
 // Import all other styles
 @import './fonts';
 @import './common/typo';