Lowercase field names required for Glue (#1387)

Co-authored-by: Kat Batuigas <kbauigas@gmail.com>

Author: kbatuigas

modules/manage/pages/iceberg/iceberg-topics-aws-glue.adoc

@@ -37,6 +37,10 @@ endif::[]
 
 == Limitations
 
+=== Lowercase field names required
+
+Use only lowercase field names. AWS Glue converts all table column names to lowercase, and Redpanda requires exact column name matches to manage schemas. Using uppercase letters prevents Redpanda from finding matching columns, which breaks schema management.
+
 === Nested partition spec support
 
 AWS Glue does not support partitioning on nested fields. If Redpanda detects that