Koel: Incomplete fix for CVE-2026-47260 — systemic SSRF in podcast & radio fetch paths

Summary The fix for CVE-2026-47260 v9.3.5 added an initial isSafeUrl check to several fetchers synchronizeEpisodes, getStreamableUrl, AddRadioStation, EpisodePlayable, but the redirect-target validation — the per-hop Guzzle onredirect callback added in follow-up commit be1e867 — was applied to on...