add_episode_to_sitemap() was removed in the previous commit, so nothing was
writing the sitemap any more. Publishing now shells out to
generate_episode_pages.py --sitemap right after the transcript is copied into
website/transcripts/, which builds the new episode's static page and rebuilds
the sitemap from the feed.
Deliberately non-fatal: by this point the audio is live on Castopod and the RSS
feed has been rebuilt, so a generator failure must not abort the publish. It
warns and moves on, and the page lands on the next run. Covered for non-zero
exit, timeout, and a missing generator script.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
