Fix semester system: 2x yearly docs, 4x yearly payments with Q4 on Sep 15

Document Submission (twice yearly):
- Q1 & Q2 documents: Due March 15 (Spring semester)
- Q3 & Q4 documents: Due September 15 (Fall semester)

Payment Schedule (quarterly):
- Q1 payments: Due March 15
- Q2 payments: Due June 15
- Q3 payments: Due September 15
- Q4 payments: Due September 15 (aligned with Fall semester docs)

This gives the desired Q4 payment due date of 15.09.2025 while maintaining
quarterly payment frequency and semester-based document submissions.

app/stiftung/management/commands/fix_advance_payment_dates.py

@@ -29,17 +29,17 @@ class Command(BaseCommand):
         
         self.stdout.write(f'Checking quarterly payments for {year} using advance payment schedule...')
         
-        # Define correct advance payment schedule
+        # Define correct quarterly payment schedule
-        advance_schedule = {
+        quarterly_schedule = {
-            f'Q1/{year}': date(year - 1, 12, 15),  # Q1 paid in December of previous year
+            f'Q1/{year}': date(year, 3, 15),       # Q1 payment due March 15
-            f'Q2/{year}': date(year, 3, 15),       # Q2 paid in March of same year  
+            f'Q2/{year}': date(year, 6, 15),       # Q2 payment due June 15  
-            f'Q3/{year}': date(year, 6, 15),       # Q3 paid in June of same year
+            f'Q3/{year}': date(year, 9, 15),       # Q3 payment due September 15
-            f'Q4/{year}': date(year, 9, 15),       # Q4 paid in September of same year
+            f'Q4/{year}': date(year, 9, 15),       # Q4 payment due September 15 (semester alignment)
         }
         
         total_fixed = 0
         
-        for quarter_desc, correct_date in advance_schedule.items():
+        for quarter_desc, correct_date in quarterly_schedule.items():
             # Find payments for this quarter that have wrong dates
             wrong_payments = DestinataerUnterstuetzung.objects.filter(
                 beschreibung__icontains=quarter_desc
@@ -81,9 +81,9 @@ class Command(BaseCommand):
                 self.style.SUCCESS(f'\n✅ Successfully fixed {total_fixed} payment due dates')
             )
         
-        # Show the advance payment schedule
+        # Show the quarterly payment schedule
-        self.stdout.write(f'\nAdvance Payment Schedule for {year}:')
+        self.stdout.write(f'\nQuarterly Payment Schedule for {year}:')
-        for quarter_desc, due_date in advance_schedule.items():
+        for quarter_desc, due_date in quarterly_schedule.items():
             self.stdout.write(f'  {quarter_desc}: Due {due_date.strftime("%B %d, %Y")}')
         
         # Check for other years that might need fixing
@@ -91,7 +91,7 @@ class Command(BaseCommand):
             other_year_payments = DestinataerUnterstuetzung.objects.filter(
                 beschreibung__regex=r'Q[1-4]/202[6-9]'
             ).exclude(
-                faellig_am__in=[date(2024, 12, 15), date(2026, 3, 15), date(2026, 6, 15), date(2026, 9, 15)]
+                faellig_am__in=[date(2026, 3, 15), date(2026, 6, 15), date(2026, 9, 15), date(2026, 9, 15)]
             ).count()
             
             if other_year_payments > 0:

app/stiftung/models.py

@@ -2752,10 +2752,10 @@ class VierteljahresNachweis(models.Model):
         if not self.faelligkeitsdatum:
             from datetime import date
             quarter_deadlines = {
-                1: date(self.jahr, 3, 15),   # Q1 deadline: March 15 (covers Q1+Q2 semester)
+                1: date(self.jahr, 3, 15),   # Q1 deadline: March 15 (Spring semester)
-                2: date(self.jahr, 6, 15),   # Q2 deadline: June 15 (auto-approved if Q1 complete)
+                2: date(self.jahr, 3, 15),   # Q2 deadline: March 15 (Spring semester, same as Q1)
-                3: date(self.jahr, 9, 15),   # Q3 deadline: September 15 (covers Q3+Q4 semester)
+                3: date(self.jahr, 9, 15),   # Q3 deadline: September 15 (Fall semester)
-                4: date(self.jahr, 12, 15),  # Q4 deadline: December 15 (auto-approved if Q3 complete)
+                4: date(self.jahr, 9, 15),   # Q4 deadline: September 15 (Fall semester, same as Q3)
             }
             self.faelligkeitsdatum = quarter_deadlines.get(self.quartal)
         

app/stiftung/views.py

@@ -7533,20 +7533,16 @@ def create_quarterly_support_payment(nachweis):
         if not default_konto:
             return None
     
-    # Calculate payment due date (advance payment schedule)
+    # Calculate payment due date (quarterly payments with Q4 aligned to semester)
-    # Payments are made in advance according to semester schedule:
+    # Q1: March 15, Q2: June 15, Q3: September 15, Q4: September 15
-    # September 15: Payment for Q4 of current year
-    # December 15: Payment for Q1 of next year  
-    # March 15: Payment for Q2 of current year
-    # June 15: Payment for Q3 of current year
     
-    if nachweis.quartal == 1:  # Q1 payment due December 15 of previous year
+    if nachweis.quartal == 1:  # Q1 payment due March 15
-        payment_due_date = date(nachweis.jahr - 1, 12, 15)
-    elif nachweis.quartal == 2:  # Q2 payment due March 15 of same year  
         payment_due_date = date(nachweis.jahr, 3, 15)
-    elif nachweis.quartal == 3:  # Q3 payment due June 15 of same year
+    elif nachweis.quartal == 2:  # Q2 payment due June 15
         payment_due_date = date(nachweis.jahr, 6, 15)
-    else:  # Q4 payment due September 15 of same year
+    elif nachweis.quartal == 3:  # Q3 payment due September 15
+        payment_due_date = date(nachweis.jahr, 9, 15)
+    else:  # Q4 payment due September 15 (same as Q3 for semester alignment)
         payment_due_date = date(nachweis.jahr, 9, 15)
     
     # Create the support payment