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

composer.json

@@ -10,6 +10,7 @@
     "require": {
         "php": "^8.2",
         "awcodes/filament-table-repeater": "^3.0",
+        "barryvdh/laravel-dompdf": "^2.0",
         "bezhansalleh/filament-shield": "^3.2",
         "filament/filament": "^3.2",
         "laravel/framework": "^11.9",