Add Vorlagen editor, upload portal, onboarding, and participant import command

- Dokument-Vorlagen-Editor: create/edit/reset document templates (admin)
- Upload-Portal: public portal for Nachweis uploads via token
- Onboarding: invite Destinatäre via email with multi-step wizard
- Bestätigungsschreiben: preview and send confirmation letters
- Email settings: SMTP configuration UI
- Management command: import_veranstaltung_teilnehmer for bulk participant import

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/templates/stiftung/destinataer_detail.html

@@ -63,6 +63,21 @@
                         </button>
                         <ul class="dropdown-menu dropdown-menu-end">
                             <li><a class="dropdown-item" href="{% url 'stiftung:destinataer_export' pk=destinataer.pk %}"><i class="fas fa-download me-2"></i>Export</a></li>
+                            <li><hr class="dropdown-divider"></li>
+                            <li>
+                                <a class="dropdown-item" href="{% url 'stiftung:bestaetigung_vorschau' pk=destinataer.pk %}" target="_blank">
+                                    <i class="fas fa-file-pdf me-2"></i>Bestätigung (Vorschau)
+                                </a>
+                            </li>
+                            <li>
+                                <form method="post" action="{% url 'stiftung:bestaetigung_versenden' pk=destinataer.pk %}" class="d-inline">
+                                    {% csrf_token %}
+                                    <button type="submit" class="dropdown-item" onclick="return confirm('Bestätigungsschreiben per E-Mail an {{ destinataer.email|default:'(keine E-Mail)'}} senden?')">
+                                        <i class="fas fa-envelope me-2"></i>Bestätigung versenden
+                                    </button>
+                                </form>
+                            </li>
+                            <li><hr class="dropdown-divider"></li>
                             <li>
                                 <form method="post" action="{% url 'stiftung:destinataer_toggle_archiv' pk=destinataer.pk %}" class="d-inline">
                                     {% csrf_token %}
@@ -493,6 +508,14 @@
                             <td>
                                 <div class="btn-group btn-group-sm">
                                     <a href="{% url 'stiftung:quarterly_confirmation_edit' nachweis.id %}" class="btn btn-outline-primary btn-sm" title="Bearbeiten"><i class="fas fa-edit"></i></a>
+                                    {% if nachweis.status == 'offen' or nachweis.status == 'teilweise' or nachweis.status == 'nachbesserung' %}
+                                        {% if destinataer.email %}
+                                        <form method="post" action="{% url 'stiftung:nachweis_aufforderung_senden' nachweis_pk=nachweis.id %}" style="display:inline;">
+                                            {% csrf_token %}
+                                            <button type="submit" class="btn btn-outline-info btn-sm" title="Upload-Aufforderung per E-Mail senden" onclick="return confirm('Upload-Link für {{ nachweis.jahr }} Q{{ nachweis.quartal }} an {{ destinataer.email }} senden?')"><i class="fas fa-paper-plane"></i></button>
+                                        </form>
+                                        {% endif %}
+                                    {% endif %}
                                     {% if user.is_staff %}
                                         {% if nachweis.status == 'eingereicht' %}
                                             <button type="button" class="btn btn-outline-success btn-sm" onclick="approveQuarterly('{{ nachweis.id }}')" title="Freigeben"><i class="fas fa-check"></i></button>