Hold episode highlights until the episode is in the Spotify feed; auto-fill study lesson audio from the feed by season + episode; v2.19.0

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

server/helpers.js

@@ -142,6 +142,7 @@ export function sanitizeFeaturedLinks(value) {
       return {
         id: typeof item.id === 'string' && item.id.trim() ? item.id.trim() : randomUUID(),
         lane: item.lane === 'second' || item.lane === 'general' ? item.lane : 'primary',
+        holdUntilReleased: item.holdUntilReleased === true,
         title: typeof item.title === 'string' ? item.title.trim().slice(0, 140) : '',
         episodeNumber: typeof item.episodeNumber === 'string' ? item.episodeNumber.trim().slice(0, 20) : '',
         summary: typeof item.summary === 'string' ? item.summary.trim().slice(0, 600) : '',