chore: add maatwebsite/excel to composer dependencies

Required for Phase 15 import/export functionality.

Co-Authored-By: Claude <noreply@anthropic.com>

Author: claude

erp/composer.json

@@ -16,6 +16,7 @@
         "laravel/reverb": "^1.10",
         "laravel/sanctum": "^4.0",
         "laravel/tinker": "^3.0",
+        "maatwebsite/excel": "^3.1",
         "pragmarx/google2fa-laravel": "^3.0",
         "spatie/laravel-permission": "^7.4",
         "tightenco/ziggy": "^2.0"