Use 5 calendar days for invoice due date

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

invoicer.py

@@ -77,13 +77,7 @@ class InvoiceInputs:
 
     @property
     def due_date(self) -> date:
-        d = self.issue_date
+        return self.issue_date + timedelta(days=5)
-        added = 0
-        while added < 5:
-            d += timedelta(days=1)
-            if d.weekday() < 5:
-                added += 1
-        return d
 
 
 def prompt_str(label: str, validator=None) -> str: