Add chunked uploads and raise storage rate to GHS 0.30/GB/month.

Large files upload in 5 MB chunks (hosting file manager pattern) for the
transfer UI and Ladill Mail S2S API, with no app-level file size cap when
TRANSFER_MAX_FILE_BYTES=0.

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

app/Http/Controllers/Transfer/FilesController.php

@@ -31,7 +31,7 @@ class FilesController extends Controller
             'files' => $files,
             'storageBytes' => (int) $storageBytes,
             'storageGb' => round($storageBytes / (1024 * 1024 * 1024), 2),
-            'pricePerGb' => (float) config('transfer.price_per_gb_month', 0.15),
+            'pricePerGb' => (float) config('transfer.price_per_gb_month', 0.30),
         ]);
     }
 }