downloadDirect fetched any caller-supplied media_url with redirect-follow
and no host/scheme validation; the route is reachable via a self-chosen
X-Recap-Install-Id, so a caller could probe the operator's LAN or cloud
metadata (169.254.169.254). Add safe-url.js: assertPublicHttpUrl rejects
non-http(s) schemes and hosts resolving to private/loopback/link-local/
reserved ranges, and safeFetch follows redirects manually, re-validating
each hop. Route downloadDirect through it (covers transcribe-url,
summarize-url, and admin-test-run).
Keysat