VideoDownloaderPing QA fixtures (test only)
/healthz            200 ok
/ok.mp4             30 MB mp4, Range supported (proxied)
/slow.mp4           61.9 MB mp4 throttled ~200 KB/s, Range supported
/cut.mp4?id=        advertises full length, aborts after ~3 MB past start (add ok=1 to serve normally)
/gone.mp4?id=N      first request 200, later 403 {"error":"expired"}; /gone.mp4/reset?id=N clears
/page-mov.html      page embedding a .mov
/page-webm.html     page embedding a .webm
/page-dotted.html   page titled "a.b.c 1.2" embedding a 1 MB mp4