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/Models/Transfer.php

@@ -79,6 +79,6 @@ class Transfer extends Model
 
     public function monthlyCostGhs(): float
     {
-        return round($this->storageGb() * (float) config('transfer.price_per_gb_month', 0.15), 2);
+        return round($this->storageGb() * (float) config('transfer.price_per_gb_month', 0.30), 2);
     }
 }