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>

config/transfer.php

@@ -1,6 +1,13 @@
 <?php
 
 return [
+    /*
+    | Service-to-service API keys (Bearer) for internal callers such as webmail.
+    */
+    'service_api_keys' => array_filter([
+        'webmail' => env('TRANSFER_API_KEY_WEBMAIL'),
+    ]),
+
     // GHS per GB per month of retention (see qr-suite-decomposition.md §7.3).
     'price_per_gb_month' => (float) env('TRANSFER_PRICE_PER_GB_MONTH', 0.15),
 
@@ -12,4 +19,7 @@ return [
 
     // Default retention when not specified (days).
     'default_retention_days' => (int) env('TRANSFER_DEFAULT_RETENTION_DAYS', 30),
+
+    // Retention for files uploaded via Ladill Mail (large attachments).
+    'mail_retention_days' => (int) env('TRANSFER_MAIL_RETENTION_DAYS', 30),
 ];