fix(tournament): filter final placements by class group count in TournamentPlacementsTab

- Introduced a new computed property to filter final placements, ensuring only classes with more than one group are displayed.
- Updated the template to reference the filtered placements, improving the clarity of the displayed tournament results.
- Adjusted logic for handling class IDs to ensure proper grouping and display of placements.

frontend/src/components/tournament/TournamentPlacementsTab.vue

@@ -7,9 +7,9 @@
             :selected-date="selectedDate"
             @update:modelValue="$emit('update:selectedViewClass', $event)"
         />
-        <section v-if="Object.keys(finalPlacementsByClass).length > 0" class="final-placements">
+        <section v-if="Object.keys(finalPlacementsByClassFiltered).length > 0" class="final-placements">
             <h3>{{ $t('tournaments.finalPlacements') }}</h3>
-            <template v-for="(classPlacements, classId) in finalPlacementsByClass" :key="`final-${classId}`">
+            <template v-for="(classPlacements, classId) in finalPlacementsByClassFiltered" :key="`final-${classId}`">
                 <div v-if="isAllSelected || shouldShowClass(classId==='null'?null:Number(classId))" class="class-section">
                     <h4 class="class-header">
                         {{ getClassName(classId) }}
@@ -86,7 +86,7 @@
                 </div>
             </template>
         </section>
-        <div v-if="Object.keys(finalPlacementsByClass).length === 0 && groupPlacements.length === 0" class="no-placements">
+        <div v-if="Object.keys(finalPlacementsByClassFiltered).length === 0 && groupPlacements.length === 0" class="no-placements">
             <p>{{ $t('tournaments.noPlacementsYet') }}</p>
         </div>
         
@@ -470,13 +470,25 @@ export default {
         groupPlacementsByClass() {
             const grouped = {};
             this.groupPlacements.forEach(p => {
-                const key = p.classId || 'null';
+                const key = p.classId != null ? String(p.classId) : 'null';
                 if (!grouped[key]) {
                     grouped[key] = [];
                 }
                 grouped[key].push(p);
             });
             return grouped;
+        },
+        /** Endplatzierung nur anzeigen, wenn die Klasse mehr als 1 Gruppe hat (Endrunde nach Gruppenphase). */
+        finalPlacementsByClassFiltered() {
+            const raw = this.finalPlacementsByClass;
+            const filtered = {};
+            for (const [classKey, placements] of Object.entries(raw)) {
+                const groupCount = (this.groupPlacementsByClass[classKey] || []).length;
+                if (groupCount > 1) {
+                    filtered[classKey] = placements;
+                }
+            }
+            return filtered;
         }
     },
     methods: {