loadMoreEpisodesForFeed's hot-cache path ran fully synchronously (no
await between getFeed and setFeeds), so the isLoadingMore spinner never
painted and keyboard input froze through every feed in a loadMoreAllFeeds
batch. Add await yieldToUI() before the setFeeds so the renderer gets a
macrotask turn to paint and process input between feeds.
Drop the "Loading…/Refreshing…/Downloading N" label text from the global
activity indicator — render the braille spinner only, per request.