Fix quarterly tracking visibility and prevent duplicate support payments

🎯 Key Changes:
- Quarterly tracking now always visible (removed studiennachweis_erforderlich condition)
- Removed automatic support payment creation when 'Unterstützung bestätigt' checkbox is checked
- Support payments now ONLY created through quarterly confirmation approval workflow
- Updated auto-creation logic to create quarterly confirmations for ALL destinataers
- Updated 'no quarterly confirmations' message to be more user-friendly

🚫 Duplicate Prevention:
- No more duplicate destinataer entries in Unterstützungen list
- Single source of truth: quarterly confirmation system controls support payment creation

📋 Template Analysis:
- Reviewed all if/else statements in quarterly tracking section
- Kept all functional logic (status checks, file existence, permissions)
- Removed only the visibility-controlling conditions

✅ Result:
- Quarterly tracking always visible regardless of study proof requirements
- Clean separation between 'Unterstützung bestätigt' checkbox and support payment creation
- Eliminates the duplicate destinataer issue reported by user

app/templates/stiftung/destinataer_detail.html

@@ -459,7 +459,6 @@
                         </div>
                         
                         <!-- Quarterly Confirmations -->
-                        {% if destinataer.studiennachweis_erforderlich %}
                         <div class="card shadow mb-4">
                             <div class="card-header bg-primary text-white">
                                 <div class="d-flex justify-content-between align-items-center">
@@ -818,13 +817,12 @@
                                 {% else %}
                                     <div class="text-center py-4">
                                         <i class="fas fa-calendar-check fa-3x text-muted mb-3"></i>
-                                        <h5 class="text-muted">Keine vierteljährlichen Nachweise</h5>
-                                        <p class="text-muted">Nachweise werden automatisch erstellt, wenn Studiennachweise erforderlich sind.</p>
+                                        <h5 class="text-muted">Keine vierteljährlichen Nachweise vorhanden</h5>
+                                        <p class="text-muted">Klicken Sie auf "Quartal hinzufügen", um einen neuen Nachweis zu erstellen.</p>
                                     </div>
                                 {% endif %}
                             </div>
                         </div>
-                        {% endif %}
                         
                         <!-- Notes Section -->
                         <div class="card shadow mb-4">