CVE-2026-6410: @fastify/static vulnerable to path traversal in directory listing

@fastify/static v9.1.0 and earlier serves directory listings outside the configured static root when the list option is enabled. A request such as /public/../outside/ causes dirList.path() to resolve a directory outside the root via path.join() without a containment check.

A remote unauthenticated attacker can obtain directory listings for arbitrary directories accessible to the Node.js process, disclosing directory names and filenames that should not be exposed. File contents are not disclosed.