change user_name still used as login and add display_name for dashboard view instead of username on login

backend/database/ERD_Dashboard_Chicken_Counting.md

@@ -57,6 +57,7 @@ erDiagram
     USER_ACCESS {
         int user_id PK "NOT NULL"
         varchar user_name "30 NOT NULL"
+        varchar display_name "30 NOT NULL"
         varchar password_hash "255 NOT NULL"
         varchar status "30 NOT NULL"
         timestamp created_at "NOT NULL"