fix(now-playing): episode as title, podcast as artist on both paths

The card put the podcast name in the title slot ('Podcast — Episode'
prefix truncating on long names) with an empty artist slot for local
playback — the downloaded files carry no artist tag. Now:
- mediaTitle is the episode title only (UI + CLI); streams keep their
  artist from stream tags, matching Apple Podcasts' title/artist layout.
- downloads are tagged at completion (ffmpeg -c copy, atomic rename):
  title=episode, artist=podcast — verified on a real 72MB file in 1.5s.

src/index.tsx

@@ -195,7 +195,7 @@ async function handlePlay(feeds: Feed[], arg: string): Promise<void> {
 				? await fetchCoverArt(coverUrl)
 				: null
 			await backend.play(episodeResult.audioUrl, {
-				mediaTitle: `${feedResult.podcast.title} — ${episodeResult.title}`,
+				mediaTitle: episodeResult.title,
 				coverArtPath: coverArtPath ?? undefined,
 			})
 			console.log("Playback started (use the UI to control)")