feat(sales): add discount support with ledger accounting

- Add discount_type column to transactions table via migration
- Update Sale model to use fillable instead of guarded for better security
- Implement discount account ledger creation when discount is applied
- Fix net amount calculation to include discount in CreateSaleAction
- Remove unused "Exempt" column from sale transaction table
- Make discount_type required when discount is enabled in form
- Update form data mutation to properly handle discount calculations

app/Actions/Sales/CreateSaleAction.php

@@ -24,7 +24,6 @@ class CreateSaleAction
         
          try {
             DB::beginTransaction();
-
             //create transactions for the sale
             app(CreateRecordTransactionsAction::class)($record, $transactions);