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/ShareDialog.tsx

@@ -281,7 +281,10 @@ function LinkShare({ job }: { job: DownloadJob }) {
       autoTried.current = true;
       create.mutate();
     }
-  }, [links.data, create]);
+    // Only links.data (empty → auto-create once) should drive this; `create` is a fresh object every
+    // render and would re-run the effect needlessly. The autoTried ref makes it fire exactly once.
+    // eslint-disable-next-line react-hooks/exhaustive-deps
+  }, [links.data]);
 
   return (
     <div>