feat: add discount management and PDF export for transmittals

- Create Discount model, migration, and Filament resource with relation to Client
- Add PDF export functionality for transmittals using DomPDF
- Include discount type selection in sales transactions
- Fix account filtering logic in expense resource
- Update export job to generate PDF instead of Excel

app/Filament/Resources/ClientResource.php

@@ -10,6 +10,7 @@ use App\Filament\Resources\ClientResource\Pages\GeneralLedger;
 use App\Filament\Resources\ClientResource\Pages\TrialBalance;
 use App\Filament\Resources\ClientResource\RelationManagers\AccountsRelationManager;
 use App\Filament\Resources\ClientResource\RelationManagers\BranchesRelationManager;
+use App\Filament\Resources\ClientResource\RelationManagers\DiscountRelationManager;
 use App\Filament\Resources\ClientResource\RelationManagers\ExpensesRelationManager;
 use App\Filament\Resources\ClientResource\RelationManagers\JournalsRelationManager;
 use App\Filament\Resources\ClientResource\RelationManagers\SalesRelationManager;
@@ -109,6 +110,7 @@ class ClientResource extends Resource
             SalesRelationManager::class,
             ExpensesRelationManager::class,
             JournalsRelationManager::class,
+            DiscountRelationManager::class,
         ];
     }