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/models.py

@@ -327,6 +327,21 @@ class Destinataer(models.Model):
         """Get the most recent funding grant"""
         return self.foerderung_set.order_by("-jahr", "-betrag").first()
 
+    @property
+    def adresse(self):
+        """Construct full address from separate fields"""
+        parts = []
+        if self.strasse:
+            parts.append(self.strasse)
+        if self.plz or self.ort:
+            city_part = []
+            if self.plz:
+                city_part.append(self.plz)
+            if self.ort:
+                city_part.append(self.ort)
+            parts.append(" ".join(city_part))
+        return "\n".join(parts) if parts else ""
+
     def erfuellt_voraussetzungen(self):
         """Prüft die Unterstützungsvoraussetzungen gemäß Angaben.
         - Abkömmling muss True sein
@@ -347,6 +362,20 @@ class Destinataer(models.Model):
         vermoegen_ok = (self.vermoegen or Decimal("0")) <= Decimal("15500")
         return bool(self.ist_abkoemmling and einkommen_ok and vermoegen_ok)
 
+    @property
+    def adresse(self):
+        """Computed address property combining strasse, plz, ort"""
+        parts = []
+        if self.strasse:
+            parts.append(self.strasse)
+        if self.plz and self.ort:
+            parts.append(f"{self.plz} {self.ort}")
+        elif self.plz:
+            parts.append(self.plz)
+        elif self.ort:
+            parts.append(self.ort)
+        return "\n".join(parts) if parts else None
+
     def naechste_studiennachweis_termine(self):
         """Gibt die nächsten beiden Stichtage (15.03, 15.09) zurück."""
         import datetime as _dt
@@ -522,6 +551,8 @@ class Land(models.Model):
         max_length=20,
         choices=ZAHLUNGSWEISE_CHOICES,
         default="jaehrlich",
+        null=True,
+        blank=True,
         verbose_name="Zahlungsweise",
     )
     pachtzins_pro_ha = models.DecimalField(
@@ -544,7 +575,12 @@ class Land(models.Model):
     # Umsatzsteuer
     ust_option = models.BooleanField(default=False, verbose_name="USt-Option")
     ust_satz = models.DecimalField(
-        max_digits=4, decimal_places=2, default=19.00, verbose_name="USt-Satz (%)"
+        max_digits=4,
+        decimal_places=2,
+        default=19.00,
+        null=True,
+        blank=True,
+        verbose_name="USt-Satz (%)"
     )
 
     # Umlagen (Durchreichungen)
@@ -2234,6 +2270,7 @@ class BackupJob(models.Model):
         ("running", "Läuft"),
         ("completed", "Abgeschlossen"),
         ("failed", "Fehlgeschlagen"),
+        ("cancelled", "Abgebrochen"),
     ]
 
     TYPE_CHOICES = [
@@ -2242,9 +2279,17 @@ class BackupJob(models.Model):
         ("files", "Nur Dateien"),
     ]
 
+    OPERATION_CHOICES = [
+        ("backup", "Backup"),
+        ("restore", "Wiederherstellung"),
+    ]
+
     id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
 
     # Job-Details
+    operation = models.CharField(
+        max_length=20, choices=OPERATION_CHOICES, default="backup", verbose_name="Vorgang"
+    )
     backup_type = models.CharField(
         max_length=20, choices=TYPE_CHOICES, verbose_name="Backup-Typ"
     )
@@ -2725,6 +2770,20 @@ class VierteljahresNachweis(models.Model):
         
         super().save(*args, **kwargs)
 
+    def get_related_support_payment(self):
+        """Get the related support payment for this quarterly confirmation"""
+        from datetime import datetime
+        
+        quarter_start = datetime(self.jahr, (self.quartal - 1) * 3 + 1, 1).date()
+        quarter_end = datetime(self.jahr, self.quartal * 3, 1).date()
+        
+        return DestinataerUnterstuetzung.objects.filter(
+            destinataer=self.destinataer,
+            faellig_am__gte=quarter_start,
+            faellig_am__lt=quarter_end,
+            beschreibung__contains=f"Q{self.quartal}/{self.jahr}"
+        ).first()
+
     @classmethod
     def get_or_create_for_period(cls, destinataer, jahr, quartal):
         """Get or create a quarterly confirmation for a specific period"""