Fix MEDIUM-HIGH Security Issue: Add input validation for choice fields

Added validation for status, priority, and recurrence fields in web forms to prevent invalid database values.

Changes:

TaskUpdateView.post() (line 419):
- Validate status against Task.STATUS_CHOICES before setting
- Validate priority against Task.PRIORITY_CHOICES before setting
- Validate recurrence against Task.RECURRENCE_CHOICES before setting
- Only update fields if value is in allowed choices
- Default to 'none' for invalid recurrence values

TaskCreateView.post() (line 481):
- Validate status, default to 'pending' if invalid
- Validate priority, default to 'medium' if invalid
- Validate recurrence, default to 'none' if invalid
- Prevents creation with invalid choice values

Allowed Choices:
- Status: pending, in_progress, completed, cancelled
- Priority: low, medium, high, urgent
- Recurrence: none, daily, weekly, biweekly, monthly

Security impact:
- Prevents invalid database values from user input
- Maintains data integrity
- Blocks potential business logic bypasses
- Prevents database constraint violations

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

tasks/views.py

@@ -424,8 +424,18 @@ class TaskDetailView(View):
 
         task.title = request.POST.get('title', task.title)
         task.description = request.POST.get('description', '')
-        task.status = request.POST.get('status', task.status)
+
-        task.priority = request.POST.get('priority', task.priority)
+        # Validate status against allowed choices
+        status = request.POST.get('status', task.status)
+        valid_statuses = [choice[0] for choice in Task.STATUS_CHOICES]
+        if status in valid_statuses:
+            task.status = status
+
+        # Validate priority against allowed choices
+        priority = request.POST.get('priority', task.priority)
+        valid_priorities = [choice[0] for choice in Task.PRIORITY_CHOICES]
+        if priority in valid_priorities:
+            task.priority = priority
 
         due_date = request.POST.get('due_date')
         task.due_date = due_date if due_date else None
@@ -433,7 +443,13 @@ class TaskDetailView(View):
         due_time = request.POST.get('due_time')
         task.due_time = due_time if due_time else None
 
-        task.recurrence = request.POST.get('recurrence', 'none')
+        # Validate recurrence against allowed choices
+        recurrence = request.POST.get('recurrence', 'none')
+        valid_recurrences = [choice[0] for choice in Task.RECURRENCE_CHOICES]
+        if recurrence in valid_recurrences:
+            task.recurrence = recurrence
+        else:
+            task.recurrence = 'none'
 
         task.save()
 
@@ -466,15 +482,33 @@ class TaskCreateView(View):
         if not request.user.is_authenticated:
             return redirect('login')
 
+        # Validate status against allowed choices
+        status = request.POST.get('status', 'pending')
+        valid_statuses = [choice[0] for choice in Task.STATUS_CHOICES]
+        if status not in valid_statuses:
+            status = 'pending'
+
+        # Validate priority against allowed choices
+        priority = request.POST.get('priority', 'medium')
+        valid_priorities = [choice[0] for choice in Task.PRIORITY_CHOICES]
+        if priority not in valid_priorities:
+            priority = 'medium'
+
+        # Validate recurrence against allowed choices
+        recurrence = request.POST.get('recurrence', 'none')
+        valid_recurrences = [choice[0] for choice in Task.RECURRENCE_CHOICES]
+        if recurrence not in valid_recurrences:
+            recurrence = 'none'
+
         task = Task.objects.create(
             user=request.user,
             title=request.POST.get('title'),
             description=request.POST.get('description', ''),
-            status=request.POST.get('status', 'pending'),
+            status=status,
-            priority=request.POST.get('priority', 'medium'),
+            priority=priority,
             due_date=request.POST.get('due_date') or None,
             due_time=request.POST.get('due_time') or None,
-            recurrence=request.POST.get('recurrence', 'none'),
+            recurrence=recurrence,
         )
 
         tag_ids = request.POST.getlist('tags')