fix: code-review round 1 — 4 findings

- og: guard safe_abs_path's None (missing/gc'd poster) before _jpeg_size, else the public /watch OG
  render crashed with an uncaught AttributeError
- channels: hoist the priority step button to module scope so it no longer remounts on every
  hold-repeat tick (which dropped the pointer capture and could let a hold run away on pointer drift)
- watch: only route audio through Web Audio on iOS (where a backgrounded <video> is suspended);
  other platforms keep their reliable native audio, avoiding a foreground-silence risk if the
  AudioContext can't resume
- share: drop the unstable `create` mutation object from the auto-create effect deps (it changes
  every render); the links.data trigger + autoTried ref already fire it exactly once

The clipboard-on-focus finding is intended (the user explicitly asked for auto-paste on focus; the
read is best-effort and browsers reject it without a gesture, so no real prompt fires).

frontend/src/components/WatchPage.tsx

@@ -25,6 +25,14 @@ function useBackgroundAudio(
   useEffect(() => {
     const video = videoRef.current;
     if (!video || !ready) return;
+    // Only iOS suspends a backgrounded <video> — and only there does rerouting the audio through
+    // Web Audio buy anything. Every other platform backgrounds media audio natively, so we leave
+    // their <video> untouched rather than risk the reroute leaving foreground audio silent if the
+    // AudioContext can't resume. (iPadOS reports as MacIntel + touch.)
+    const isIOS =
+      /iP(hone|ad|od)/.test(navigator.userAgent) ||
+      (navigator.platform === "MacIntel" && navigator.maxTouchPoints > 1);
+    if (!isIOS) return;
     const wire = () => {
       if (wiredRef.current) {
         ctxRef.current?.resume().catch(() => {});