Enhanced quarterly confirmation system with approval workflow and export improvements

Features added:
- ✅ Fixed quarterly confirmation approval system with URL pattern
- ✅ Added re-approval and status reset functionality for quarterly confirmations
- ✅ Synchronized quarterly approval status with support payment system
- ✅ Enhanced Destinataer export with missing fields (anrede, titel, mobil)
- ✅ Added quarterly confirmation data and documents to export system
- ✅ Fixed address field display issues in destinataer template
- ✅ Added quarterly statistics dashboard to support payment lists
- ✅ Implemented duplicate support payment prevention and cleanup
- ✅ Added visual indicators for quarterly-linked support payments

Technical improvements:
- Enhanced create_quarterly_support_payment() with duplicate detection
- Added get_related_support_payment() method to VierteljahresNachweis model
- Improved quarterly confirmation workflow with proper status transitions
- Added computed address property to Destinataer model
- Fixed template field mismatches (anrede, titel, mobil vs strasse, plz, ort)
- Enhanced backup system with operation tracking and cancellation

Workflow enhancements:
- Quarterly confirmations now properly sync with support payments
- Single support payment per destinataer per quarter (no duplicates)
- Approval button works for both eingereicht and geprueft status
- Reset functionality allows workflow restart
- Export includes complete quarterly data with uploaded documents

app/stiftung/urls.py

@@ -262,6 +262,11 @@ urlpatterns = [
         name="backup_download",
     ),
     path("administration/backup/restore/", views.backup_restore, name="backup_restore"),
+    path(
+        "administration/backup/<uuid:backup_id>/cancel/",
+        views.backup_cancel,
+        name="backup_cancel",
+    ),
     path(
         "administration/unterstuetzungen/",
         views.unterstuetzungen_list,
@@ -364,4 +369,14 @@ urlpatterns = [
         views.quarterly_confirmation_update,
         name="quarterly_confirmation_update",
     ),
+    path(
+        "quarterly-confirmations/<uuid:pk>/approve/",
+        views.quarterly_confirmation_approve,
+        name="quarterly_confirmation_approve",
+    ),
+    path(
+        "quarterly-confirmations/<uuid:pk>/reset/",
+        views.quarterly_confirmation_reset,
+        name="quarterly_confirmation_reset",
+    ),
 ]