Fix payment system balance integration and add calendar functionality

- Implement automated payment tracking with Django signals
- Fix duplicate transaction creation with unique referenz system
- Add calendar system with CRUD operations and event management
- Reorganize navigation menu (rename sections, move admin functions)
- Replace Geschichte editor with EasyMDE markdown editor
- Add management commands for balance reconciliation
- Create missing transactions for previously paid payments
- Ensure account balances accurately reflect all payment activity

Features added:
- Calendar entries creation and administration via menu
- Payment status tracking with automatic balance updates
- Duplicate prevention for payment transactions
- Markdown editor with live preview for Geschichte pages
- Database reconciliation tools for payment/balance sync

Bug fixes:
- Resolved IntegrityError on payment status changes
- Fixed missing account balance updates for paid payments
- Prevented duplicate balance deductions on re-saves
- Corrected menu structure and admin function placement

app/templates/stiftung/geschichte/detail.html

@@ -67,7 +67,7 @@
             </div>
             <div class="card-body">
                 <div class="geschichte-content">
-                    {{ seite.inhalt|linebreaks }}
+                    {{ seite.inhalt|markdown_to_html }}
                 </div>
                 
                 {% if bilder %}
@@ -75,13 +75,22 @@
                     <h4><i class="fas fa-images me-2"></i>Bildergalerie</h4>
                     {% for bild in bilder %}
                     <div class="geschichte-bild">
-                        <img src="{{ bild.bild.url }}" alt="{{ bild.alt_text|default:bild.titel }}" class="img-fluid">
-                        <div class="bild-beschreibung">
-                            <strong>{{ bild.titel }}</strong>
-                            {% if bild.beschreibung %}
-                            <br>{{ bild.beschreibung }}
+                        <div class="d-flex justify-content-between align-items-start mb-2">
+                            <h6 class="mb-0">{{ bild.titel }}</h6>
+                            {% if perms.stiftung.delete_geschichtebild %}
+                            <a href="{% url 'stiftung:geschichte_bild_delete' slug=seite.slug bild_id=bild.id %}" 
+                               class="btn btn-outline-danger btn-sm" 
+                               title="Bild löschen">
+                                <i class="fas fa-trash"></i>
+                            </a>
                             {% endif %}
                         </div>
+                        <img src="{{ bild.bild.url }}" alt="{{ bild.alt_text|default:bild.titel }}" class="img-fluid">
+                        {% if bild.beschreibung %}
+                        <div class="bild-beschreibung mt-2">
+                            {{ bild.beschreibung }}
+                        </div>
+                        {% endif %}
                     </div>
                     {% endfor %}
                 </div>