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>

app/Http/Controllers/Api/ChunkedUploadController.php

@@ -140,7 +140,8 @@ class ChunkedUploadController extends Controller
                 'id' => $transfer->id,
                 'title' => $transfer->title,
                 'public_url' => $transfer->qrCode?->publicUrl(),
-                'expires_at' => $transfer->expires_at?->toIso8601String(),
+                'paid_until' => $transfer->paid_until?->toIso8601String(),
+                'expires_at' => $transfer->paid_until?->toIso8601String(),
                 'files' => $transfer->files->map(fn ($file) => [
                     'name' => $file->original_name,
                     'size_bytes' => $file->size_bytes,