Feature: Add ACS courier integration

ACS rate driver (live price quotes via ACS_Price_Calculation, cached postcode-to-station lookups) and fulfillment service (voucher creation, label printing, end-of-day pickup manifest). Adds a per-rate pricing_mode column so admins can choose live API pricing vs. a fixed price on ACS-driven shipping rates, surfaced via a custom Rates page.

src/Shipping/Carriers/Acs/AcsClient.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace Modules\Core\Shipping\Carriers\Acs;
+
+use Illuminate\Support\Facades\Http;
+
+class AcsClient
+{
+    public function __construct(private readonly array $config) {}
+
+    public function call(string $alias, array $parameters = []): AcsResponse
+    {
+        $response = Http::withHeaders([
+            'AcsApiKey' => $this->config['api_key'],
+        ])
+            ->timeout($this->config['timeout'])
+            ->post($this->config['base_url'], [
+                'ACSAlias' => $alias,
+                'ACSInputParameters' => array_merge($this->credentialParams(), $parameters),
+            ]);
+
+        return AcsResponse::fromHttpResponse($response);
+    }
+
+    private function credentialParams(): array
+    {
+        return [
+            'Company_ID' => $this->config['company_id'],
+            'Company_Password' => $this->config['company_password'],
+            'User_ID' => $this->config['user_id'],
+            'User_Password' => $this->config['user_password'],
+        ];
+    }
+}