[ROMM-1452] Mark naive datetimes as UTC

backend/endpoints/responses/base.py

@@ -0,0 +1,18 @@
+from datetime import datetime, timezone
+
+from pydantic import BaseModel as PydanticBaseModel
+from pydantic import ConfigDict
+
+
+class BaseModel(PydanticBaseModel):
+    """Ensures all datetime fields include UTC timezone"""
+
+    model_config = ConfigDict(
+        json_encoders={
+            datetime: lambda dt: (
+                dt.isoformat()
+                if dt.tzinfo
+                else dt.replace(tzinfo=timezone.utc).isoformat()
+            )
+        }
+    )