gotenberg_host was validated only with Laravel's 'url' rule, which permits
loopback/private/link-local hosts (e.g. http://127.0.0.1, http://10.0.0.1,
the cloud metadata endpoint http://169.254.169.254). When a PDF renders, the
server POSTs the document HTML to that host — an SSRF primitive.
- Adds App\Rules\SafeRemoteUrl: requires http(s) and rejects any host that
resolves to a loopback/private/link-local/CGNAT/reserved address (IPv4 and
IPv6), including literal-IP hosts.
- Wires it into PDFConfigurationRequest for gotenberg_host.
- Adds a defensive re-check in GotenbergPDFDriver before the outbound call to
cover hosts set via env/seed/stale config or DNS rebinding (TOCTOU).
Adds unit tests for the rule + validator integration.
