[BUG] Should use $host instead of $http_host for x-original-url #136

The Nginx Proxy Manager and SWAG documentation currently builds X-Original-URL using $http_host. Since $http_host can differ from the host Nginx uses for routing absolute-form requests, the examples should use $host instead to keep routing and Tinyauth's app/ACL lookup consistent.

Thank you @bsaurusrex for the report.