feat: add task deletion for all users

app/services/tasks.py

@@ -157,3 +157,17 @@ def create_quick_task(title: str, effort: str, creator: User, description: str =
     db.session.add(task)
     db.session.commit()
     return task
+
+
+def delete_task_instance(task: TaskInstance) -> None:
+    template = task.task_template
+    db.session.delete(task)
+    db.session.flush()
+
+    remaining_instance = db.session.scalar(
+        select(TaskInstance.id).where(TaskInstance.task_template_id == template.id).limit(1)
+    )
+    if remaining_instance is None:
+        db.session.delete(template)
+
+    db.session.commit()