Keep a Substack subtitle above the post

Substack puts a post's subtitle in <description> and leaves it out of
content:encoded, and body() took content:encoded alone, so the subtitle
was lost (a known gap in CLAUDE.md). A description is now shown above the
body, as <p><em>, when it is short plain text the body does not already
contain. Podcast feeds that repeat their notes in both, whole or cut short
with an ellipsis, are unchanged; the comparison is by words, since a tag
taken out of the body leaves stray spaces around punctuation.

Checked against Experimental History's feed (subtitles appear) and The
Daily's (notes in both fields, shown once). Entries are inserted with ON
CONFLICT DO NOTHING, so only posts first seen from now on get it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -12,6 +12,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - The daemon no longer prints the web token when it starts, so it stays out of `docker logs`. It
   says where the token is kept instead: `[web] token` in config.toml.
 
+### Fixed
+
+- A Substack post shows its subtitle above the post, as Substack does. Only posts that arrive from
+  now on have it.
+
 ## [0.8.2] - 2026-09-19
 
 ### Added