Items written in Markdown show formatted (#284)

A description with Markdown and no HTML tag is rendered to HTML with
pulldown-cmark, and an item with no text but RSS's <source:markdown>
(https://source.scripting.com/, as Scripting News sends beside its HTML) uses
that. HTML is left alone, and plain text without Markdown in it stays as it
was, so a line like "1984. ..." is not made a list. ammonia cleans the result
as any feed's HTML. Stored items keep what they have: the scanner does not
rewrite an item it has.

Reference: http://scripting.com/2026/10/06/005559.html

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/directory/CHANGELOG.md

@@ -10,6 +10,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- A feed's items written in Markdown show formatted on its page, from a Markdown description or RSS's `<source:markdown>` (#284).
+
 ### Security
 
 - ammonia, which cleans publishers' HTML, updated to 4.2.4 for three advisories, among them XSS through SVG animation tags; rustls to 0.23.46 for five and h2 to 0.4.20 for one (#281).