Add service API for Ladill Mail large attachment uploads.

Webmail can POST /api/v1/transfers with a mailbox address to create share links for files above 25 MB.

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

app/Services/Identity/MailboxUserResolver.php

@@ -0,0 +1,58 @@
+<?php
+
+namespace App\Services\Identity;
+
+use App\Models\User;
+use Illuminate\Support\Facades\Http;
+use RuntimeException;
+
+/** Resolves a Ladill Transfer user mirror for a mailbox address (webmail integration). */
+class MailboxUserResolver
+{
+    public function resolve(string $mailbox): User
+    {
+        $mailbox = strtolower(trim($mailbox));
+        if ($mailbox === '' || ! str_contains($mailbox, '@')) {
+            throw new RuntimeException('Invalid mailbox address.');
+        }
+
+        $existing = User::query()->where('email', $mailbox)->first();
+        if ($existing) {
+            return $existing;
+        }
+
+        $base = rtrim((string) config('identity.api_url'), '/');
+        $key = (string) config('identity.api_key');
+        if ($base === '' || $key === '') {
+            throw new RuntimeException('Identity API is not configured.');
+        }
+
+        $res = Http::withToken($key)
+            ->acceptJson()
+            ->timeout(10)
+            ->get("{$base}/identity/profile", ['mailbox' => $mailbox]);
+
+        if ($res->failed()) {
+            throw new RuntimeException('Could not resolve the Ladill account for this mailbox.');
+        }
+
+        $data = $res->json('data');
+        if (! is_array($data)) {
+            throw new RuntimeException('Could not resolve the Ladill account for this mailbox.');
+        }
+
+        $publicId = trim((string) ($data['public_id'] ?? ''));
+        if ($publicId === '') {
+            throw new RuntimeException('No Ladill account is linked to this mailbox.');
+        }
+
+        return User::updateOrCreate(
+            ['public_id' => $publicId],
+            [
+                'name' => trim((string) ($data['name'] ?? '')) ?: $mailbox,
+                'email' => $mailbox,
+                'avatar_url' => ($picture = trim((string) ($data['picture'] ?? ''))) !== '' ? $picture : null,
+            ],
+        );
+    }
+}