fix: always navigate to Series screen when exiting playback from Episode

Instead of just popping the EpisodeRoute (which could land on Home if
opened from ContinueWatching), pop and push a SeriesRoute so playback
exit consistently returns to the SeriesScreen.

app/src/main/java/hu/bbara/purefin/app/content/episode/EpisodeScreen.kt

@@ -69,7 +69,7 @@ fun EpisodeScreen(
         episode = episode.value!!,
         downloadState = downloadState.value,
         onBack = viewModel::onBack,
-        onPlaybackStarted = viewModel::onBack,
+        onPlaybackStarted = viewModel::onPlaybackStarted,
         onDownloadClick = onDownloadClick,
         modifier = modifier
     )