Fix recurring task duplication bug

Prevent process_recurring_tasks from creating duplicate tasks for dates that already have completed instances. Previously only checked for pending tasks, causing old completed recurring tasks to reappear as pending when subsequent instances went overdue.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

notifications/tasks.py

@@ -161,12 +161,12 @@ def process_recurring_tasks():
         next_due_date = task.calculate_next_due_date()
         if next_due_date:
             # Check if we already created this recurrence
+            # Check for any task (pending OR completed) to avoid duplicates
             existing = Task.objects.filter(
                 user=task.user,
                 title=task.title,
                 due_date=next_due_date,
-                recurrence=task.recurrence,
-                status='pending'
+                recurrence=task.recurrence
             ).exists()
 
             if not existing: