fix(r5): address the second /code-review high round — 7 findings

- the volume keys no longer defer to a scrollable card while in fullscreen
  (mirrored into a ref: the keydown handler is bound once and state would be stale)
- the debounced volume flush writes straight to storage; persisting inside a
  setState updater is not guaranteed to run for an unmounting component
- the HLS sweep also matches the original {key}_{start} directory naming, which
  is what the oldest leftovers on disk actually use
- run_rss_poll returns {new, failed} so an egress outage stops rendering as
  "ok — 0" in the scheduler card and the audit log; /api/sync/rss reports it too
- drop the unused poll_rss_channel (it silently gained a new exception)
- _Breaker.run is generic, so a call site keeps its item-id type
- test helper instead of the generator-throw idiom

backend/app/routes/sync.py

@@ -52,8 +52,10 @@ def sync_subscriptions(
 def sync_rss(
     user: User = Depends(require_human), db: Session = Depends(get_db)
 ) -> dict:
-    new = run_rss_poll(db, _user_channels(db, user))
-    return {"new_videos": new}
+    result = run_rss_poll(db, _user_channels(db, user))
+    # `failed` = feeds that could not be read at all (see run_rss_poll); surfaced so a manual poll
+    # reports an outage instead of an innocent-looking "0 new".
+    return {"new_videos": result["new"], "failed_feeds": result["failed"]}
 
 
 @router.post("/backfill")