Add Ladill POS v1 — register, Pay checkout, and commerce links.

Staff-facing counter register at pos.ladill.com with catalog cart, cash and
MoMo/card checkout via Ladill Pay, CRM timeline/import, invoice prefill, and
Merchant catalog import.

Co-authored-by: Cursor <cursoragent@cursor.com>

config/billing.php

@@ -0,0 +1,10 @@
+<?php
+
+return [
+    'api_url' => env('BILLING_API_URL', 'https://ladill.com/api/billing'),
+    'api_key' => env('BILLING_API_KEY_POS'),
+    'service' => 'pos',
+    'wallet_balance_route' => 'wallet.balance',
+    'currency' => 'GHS',
+    'platform_settings_connection' => env('BILLING_PLATFORM_SETTINGS_CONNECTION', 'platform'),
+];