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>

package.json

@@ -1,7 +1,7 @@
 {
   "name": "siteforge",
   "private": true,
-  "version": "2.18.0",
+  "version": "2.19.0",
   "type": "module",
   "scripts": {
     "dev": "vite",