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>

app/Services/Identity/IdentityClient.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace App\Services\Identity;
+
+use Illuminate\Support\Facades\Http;
+
+class IdentityClient
+{
+    /** @return array<string, mixed> */
+    public function mailboxLinkStatus(string $publicId): array
+    {
+        $response = $this->request()->get($this->url('/identity/mailbox-link'), [
+            'user' => $publicId,
+        ]);
+
+        $response->throw();
+
+        return (array) $response->json('data', []);
+    }
+
+    /** @return array<string, mixed> */
+    public function linkMailbox(string $publicId, string $mailboxAddress): array
+    {
+        $response = $this->request()->put($this->url('/identity/mailbox-link'), [
+            'user' => $publicId,
+            'mailbox_address' => $mailboxAddress,
+        ]);
+
+        $response->throw();
+
+        return (array) $response->json('data', []);
+    }
+
+    /** @return array<string, mixed> */
+    public function unlinkMailbox(string $publicId): array
+    {
+        $response = $this->request()->delete($this->url('/identity/mailbox-link'), [
+            'user' => $publicId,
+        ]);
+
+        $response->throw();
+
+        return (array) $response->json('data', []);
+    }
+
+    private function request()
+    {
+        return Http::withToken((string) config('identity.api_key'))
+            ->acceptJson()
+            ->timeout(15);
+    }
+
+    private function url(string $path): string
+    {
+        return rtrim((string) config('identity.api_url'), '/').$path;
+    }
+}