Refactor 'download' field to 'discharge' across models and services

- Renamed the 'download' field to 'discharge' in the FaLineItem model and updated related services and schemas accordingly.
- Adjusted frontend components to reflect the new 'discharge' terminology.
- Ensured consistency in filtering and validation logic across the application to use the updated field name.

frontend/src/lib/api/dashboard/a76/items.ts

@@ -127,7 +127,7 @@ export interface FaLineItem {
     subitem_number?: number;
 
     // Special flags
-    download?: boolean;
+    discharge?: boolean;
     own_equipment?: boolean;
     omit_annex31?: boolean;