Add transfer data fields to payment form

- Added empfaenger_iban, empfaenger_name, verwendungszweck to DestinataerUnterstuetzungForm
- Made faellig_am read-only for automatically generated quarterly payments
- Added proper placeholders for transfer data fields
- Template already supports these fields in Überweisungsdaten section

app/stiftung/forms.py

@@ -969,6 +969,9 @@ class DestinataerUnterstuetzungForm(forms.ModelForm):
             "faellig_am",
             "status",
             "beschreibung",
+            "empfaenger_iban",
+            "empfaenger_name", 
+            "verwendungszweck",
         ]
         widgets = {
             "destinataer": forms.Select(attrs={"class": "form-select"}),
@@ -981,8 +984,26 @@ class DestinataerUnterstuetzungForm(forms.ModelForm):
             ),
             "status": forms.Select(attrs={"class": "form-select"}),
             "beschreibung": forms.TextInput(attrs={"class": "form-control"}),
+            "empfaenger_iban": forms.TextInput(
+                attrs={"class": "form-control", "placeholder": "DE89 3704 0044 0532 0130 00"}
+            ),
+            "empfaenger_name": forms.TextInput(
+                attrs={"class": "form-control", "placeholder": "Max Mustermann"}
+            ),
+            "verwendungszweck": forms.TextInput(
+                attrs={"class": "form-control", "placeholder": "Vierteljährliche Unterstützung Q1/2025"}
+            ),
         }
 
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        
+        # Make faellig_am read-only for automatically generated quarterly payments
+        if self.instance and self.instance.pk and self.instance.beschreibung:
+            if "Vierteljährliche Unterstützung" in self.instance.beschreibung and "(automatisch erstellt)" in self.instance.beschreibung:
+                self.fields['faellig_am'].widget.attrs['readonly'] = True
+                self.fields['faellig_am'].help_text = "Fälligkeitsdatum wird automatisch basierend auf Quartal berechnet"
+
 
 class DestinataerNotizForm(forms.ModelForm):
     class Meta: