This routes external downloads used by webhook fetch used by macros and
acutomations through SafeFetch. It closes the SSRF exposure from raw
Down.download paths, preserves provider-specific auth and header flows,
and adds regression coverage for blocked internal URLs plus
authenticated downloads.
Fixes # (issue):
[CW-6940](https://linear.app/chatwoot/issue/CW-6940/ssrf-via-webhooksautomationmacros-non-upload-non-avatar)