feat: add is_chat field to board memory and task_id to approvals, update pagination and response models

backend/app/api/board_onboarding.py

@@ -2,7 +2,6 @@ from __future__ import annotations
 
 import logging
 import re
-from datetime import datetime
 from uuid import uuid4
 
 from fastapi import APIRouter, Depends, HTTPException, status