fix(backfill): add sys.path insertion for module resolution

scripts/backfill_chapter_content_refs.py

@@ -4,10 +4,13 @@ import argparse
 import asyncio
 import hashlib
 import json
+import sys
 from pathlib import Path
 from bson import ObjectId
 from sqlalchemy import text
 
+sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
+
 from app.config import settings
 from app.database import SessionLocal, mongo_db
 from app.storage import storage