Add BunnyCDN integration, on-air website badge, publish script fixes

- On-air toggle uploads status.json to BunnyCDN + purges cache, website
  polls it every 15s to show live ON AIR / OFF AIR badge
- Publish script downloads Castopod's copy of audio for CDN upload
  (byte-exact match), removes broken slug fallback, syncs all episode
  media to CDN after publishing
- Fix f-string syntax error in publish_episode.py (Python <3.12)
- Enable CORS on BunnyCDN pull zone for json files
- CDN URLs for website OG images, stem recorder bug fixes, LLM token
  budget tweaks, session context in CLAUDE.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

website/how-it-works.html

@@ -9,7 +9,7 @@
 
   <meta property="og:title" content="How It Works — Luke at the Roost">
   <meta property="og:description" content="The tech behind a one-of-a-kind AI radio show. Real callers, AI callers, voice synthesis, and a live control room.">
-  <meta property="og:image" content="https://podcast.macneilmediagroup.com/media/podcasts/LukeAtTheRoost/cover_feed.png?v=3">
+  <meta property="og:image" content="https://cdn.lukeattheroost.com/media/podcasts/LukeAtTheRoost/cover_feed.png?v=3">
   <meta property="og:url" content="https://lukeattheroost.com/how-it-works">
   <meta property="og:type" content="website">