Bill transfer storage monthly with a 15-day grace period before deletion.

Files stay available while wallet renewals succeed each month. Failed renewals
keep files for TRANSFER_GRACE_PERIOD_DAYS (default 15) before automatic cleanup.

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

tests/Concerns/FakesTransferBilling.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Tests\Concerns;
+
+use Illuminate\Support\Facades\Http;
+
+trait FakesTransferBilling
+{
+    protected function fakeTransferBillingApi(): void
+    {
+        $base = rtrim((string) config('billing.api_url'), '/');
+
+        Http::fake([
+            $base.'/can-afford*' => Http::response(['affordable' => true]),
+            $base.'/debit*' => Http::response(['ok' => true]),
+            $base.'/balance*' => Http::response(['balance_minor' => 100000]),
+            $base.'/service-ledger*' => Http::response([
+                'spent_minor' => 0,
+                'credited_minor' => 0,
+                'net_minor' => 0,
+            ]),
+        ]);
+    }
+}