Transmute has full-read SSRF in URL file import (POST /api/files/url) — no host/IP validation, follows redirects

Transmute is a free, open-source, self-hosted file conversion and compression tool. Prior to version 1.3.0, Transmute's URL import endpoint, `POST /api/files/url`, is vulnerable to Server-Side Request Forgery (SSRF). The HTTP downloader used by this endpoint fetches user-supplied URLs with redirects enabled and does not validate whether the target resolves to a public, external address. As a result, an authenticated user (or guest user if they are enabled) may be able to cause the Transmute server to make HTTP requests to internal or cloud-local resources from the server's network position. Because downloaded content is stored and can later be retrieved through `GET /api/files/{id}`, this issue can result in full-read SSRF rather than blind SSRF. This is fixed in version 1.3.0.