feat: update default persistence to MongoDB and enhance configuration options

backend/db/db.py

@@ -25,7 +25,7 @@ except ImportError:  # pragma: no cover - pymongo is a required dependency
     ASCENDING = 1
 
 
-USE_MONGODB = os.environ.get('USE_MONGODB', 'false').lower() == 'true'
+USE_MONGODB = os.environ.get('USE_MONGODB', 'true').lower() == 'true'
 # Resolve the MongoDB database name once at module load so runtime changes to
 # DB_ENV/DATA_ENV in tests do not switch databases mid-process.
 _mongo_db_name = get_mongo_db_name() if USE_MONGODB else None

backend/scripts/migrate_to_mongodb.py

@@ -184,7 +184,7 @@ def main():
     )
     args = parser.parse_args()
 
-    if os.environ.get('USE_MONGODB', 'false').lower() != 'true':
+    if os.environ.get('USE_MONGODB', 'true').lower() != 'true':
         print('Set USE_MONGODB=true to run the migration.', file=sys.stderr)
         sys.exit(1)
 

backend/tests/test_mongo_adapter.py

@@ -15,7 +15,7 @@ from db.mongo_client import get_mongo_client, get_mongo_db_name
 
 # All tests in this module require the mongomock-backed MongoDB adapter.
 pytestmark = pytest.mark.skipif(
-    os.environ.get('USE_MONGODB', 'false').lower() != 'true',
+    os.environ.get('USE_MONGODB', 'true').lower() != 'true',
     reason='MongoDB adapter tests require USE_MONGODB=true',
 )