Fix download status handling and the blank page after download

- Never let a non-authoritative MeTube 'updated' event downgrade a
  terminal job (it refilled the progress bar after completion).
- Self-heal stale active jobs against MeTube history on status polls,
  so a missed event no longer leaves a job stuck in 'queued'.
- Build YT.Player on an imperatively created child div: React keeps
  owning the container, so switching to the local copy after a
  download no longer throws removeChild and blanks the page.
- Autoplay on open and seek controls; subtitle experiment reverted.

frontend/src/App.css

@@ -185,6 +185,7 @@ button, .button-primary, .button-secondary, .button-quiet, .button-danger { tran
 .player-wrapper iframe, .player-wrapper video { position: absolute; inset: 0; width: 100%; height: 100%; border: 0; background: #000; }
 .player-wrapper video { touch-action: manipulation; }
 .yt-player-host { position: absolute; inset: 0; }
+.yt-player-host > div { width: 100%; height: 100%; }
 .video-page-meta-row { display: flex; align-items: center; justify-content: space-between; gap: 8px 16px; flex-wrap: wrap; margin: 11px 0 22px; }
 .video-page-meta-row .video-page-source { margin: 0; }
 .video-page-source { color: var(--muted); font-size: 12px; }

frontend/src/components/Player.tsx

@@ -153,12 +153,15 @@ function Player({ video }: Props) {
   }, [useLocal])
 
   // YouTube-ветка: динамическая идемпотентная загрузка IFrame Player API,
-  // создание YT.Player в host-div с nocookie-хостом, фолбэк на plain-iframe по таймауту.
+  // создание YT.Player на императивном дочернем div в host-div (YT.Player заменяет
+  // переданный элемент iframe'ом, React управляет только контейнером), nocookie-хост,
+  // фолбэк на plain-iframe по таймауту.
   useEffect(() => {
     if (useLocal) return
     let cancelled = false
     let timedOut = false
     let timeoutId: number | null = null
+    let child: HTMLDivElement | null = null
     ytPlayerRef.current?.destroy()
     ytPlayerRef.current = null
 
@@ -167,6 +170,8 @@ function Player({ video }: Props) {
       timedOut = true
       ytPlayerRef.current?.destroy()
       ytPlayerRef.current = null
+      if (child?.parentNode) child.remove()
+      child = null
       if (!cancelled) setYtApiStatus('timeout')
     }, YT_API_TIMEOUT_MS)
 
@@ -175,7 +180,9 @@ function Player({ video }: Props) {
         if (cancelled || timedOut || !window.YT?.Player) return
         const host = ytHostRef.current
         if (!host) return
-        const player = new window.YT.Player(host, {
+        child = document.createElement('div')
+        host.appendChild(child)
+        const player = new window.YT.Player(child, {
           videoId: video.youtube_video_id,
           host: 'https://www.youtube-nocookie.com',
           playerVars: { playsinline: 1, autoplay: 1 },
@@ -206,6 +213,8 @@ function Player({ video }: Props) {
       if (timeoutId !== null) window.clearTimeout(timeoutId)
       ytPlayerRef.current?.destroy()
       ytPlayerRef.current = null
+      if (child?.parentNode) child.remove()
+      child = null
     }
   }, [useLocal, video.youtube_video_id])