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.js

@@ -67,6 +67,7 @@ import { register as registerNuggets } from './server/routes/nuggets.js'
 import { register as registerNuggetsHostUpload } from './server/routes/nuggets-host-upload.js'
 import { register as registerNuggetsWorkflow } from './server/routes/nuggets-workflow.js'
 import { register as registerPodcastWorkflow } from './server/routes/podcast-workflow.js'
+import { warmFeedSnapshot } from './server/feed-release.js'
 import { preferIpv4ForSeafile } from './server/seafile-dns.js'
 import { startNuggetsSeafileWatcher } from './server/nuggets-seafile-watcher.js'
 import { register as registerFeed } from './server/routes/feed.js'
@@ -208,6 +209,7 @@ Promise.all([
     }, BACKUP_INTERVAL_MS)
 
     startNuggetsSeafileWatcher()
+    warmFeedSnapshot()
 
     // Purge expired study sessions every hour
     setInterval(() => {