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/DiscountResource/Pages/CreateDiscount.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace App\Filament\Resources\DiscountResource\Pages;
+
+use App\Filament\Resources\DiscountResource;
+use Filament\Actions;
+use Filament\Resources\Pages\CreateRecord;
+
+class CreateDiscount extends CreateRecord
+{
+    protected static string $resource = DiscountResource::class;
+}