Default task sort to due date instead of raw model order

The "Default" option cleared the sort param and fell back to the
model's Meta.ordering (sort_order, -priority, due_date, created_at),
which read as broken/unsorted to users. Default is now due date
(earliest first), matching the existing due_date sort option.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tasks/views.py

@@ -232,7 +232,7 @@ class DashboardView(View):
         current_filter = request.GET.get('filter', 'all')
         current_tag_id = request.GET.get('tag')
         selected_task_id = request.GET.get('selected')
-        current_sort = request.GET.get('sort', 'default')
+        current_sort = request.GET.get('sort', 'due_date')
 
         # Base query
         tasks = Task.objects.filter(