fix(TournamentGroupsTab): allow empty values in max group size input normalization

- Updated the normalization function in TournamentGroupsTab to permit empty values for max group size input, enhancing flexibility for user input.
- This change improves the user experience by allowing users to clear the input field without triggering validation errors.

frontend/src/components/tournament/TournamentGroupsTab.vue

@@ -348,7 +348,7 @@ export default {
             this.$emit('modus-change');
         },
         onMaxGroupSizeBlur(rawValue) {
-            const normalized = this.normalizeNumberInput(rawValue, { min: 1, allowEmpty: false });
+            const normalized = this.normalizeNumberInput(rawValue, { min: 1, allowEmpty: true });
             this.$emit('update:maxGroupSize', normalized);
         },
         groupRankingsForGroup(group) {