Cloudreve WebDAV (`/dav`) has Path Traversal / Broken Access Control — scoped DAV credential escapes its configured account root

Summary A Cloudreve WebDAV account stores a uri that defines the account's root folder. The WebDAV request handler stripPrefix in pkg/webdav/webdav.go trims the /dav prefix from the request path and joins the remainder to that root with fs.URI.JoinRaw, but never checks that the joined URI stays...