One article header everywhere: rubric, why block, then the summary

The web index, the article page and both EPUB pages each ordered the same
metadata differently, and the "understanding" line was one wall of text
with the why line above it on one page and below it on another. Every
surface now reads title, meta, rubric, why block, summary:

- the rubric is a newspaper kicker (topic group and format in small caps)
  followed by the specific topics; depth and technicality stay on the
  dashboard article page only
- the accent-bar why block holds the editor's line and "Matches: …" (the
  matched interests) beneath it
- the social line moves after the summary on the article page and chapter,
  matching the index pages, and the EPUB chapter footer no longer carries
  the understanding line

`understanding_line` becomes an `Understanding { kicker, topics, interests }`
struct shared by the web view models and the EPUB, and the three web
templates include one `_understanding.html` partial.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NxctvrEPQZ9pX58LRgGYNZ

src/epub/templates/chapter.xhtml

@@ -7,15 +7,25 @@
         <p class="byline">{{ line }}</p>
 {% endif %}
         <p class="meta">{{ meta_line }}</p>
-{% if let Some(text) = why %}
-        <p class="why"><em>Why it&#39;s here: {{ text }}</em></p>
+{% if understanding.kicker.is_some() || understanding.topics.is_some() %}
+        <p class="rubric">{% if let Some(kicker) = understanding.kicker %}<span class="kicker">{{ kicker }}</span>{% if let Some(topics) = understanding.topics %} &#160; {{ topics }}{% endif %}{% else %}{% if let Some(topics) = understanding.topics %}{{ topics }}{% endif %}{% endif %}</p>
 {% endif %}
-{% if let Some(line) = social_line %}
-        <p class="social">{{ line }}</p>
+{% if why.is_some() || understanding.interests.is_some() %}
+        <div class="why">
+{% if let Some(text) = why %}
+          <p class="why-line"><em>Why it&#39;s here: {{ text }}</em></p>
+{% endif %}
+{% if let Some(interests) = understanding.interests %}
+          <p class="why-matches">Matches: {{ interests }}</p>
+{% endif %}
+        </div>
 {% endif %}
 {% if let Some(text) = summary %}
         <p class="summary">{{ text }}</p>
 {% endif %}
+{% if let Some(line) = social_line %}
+        <p class="social">{{ line }}</p>
+{% endif %}
 {% if excerpt_only %}
         <p class="notice">(excerpt only &#8212; read online)</p>
 {% endif %}
@@ -26,9 +36,6 @@
       </div>
       <hr class="rule"/>
       <div class="article-footer">
-{% if let Some(line) = understanding %}
-        <p class="understood">{{ line }}</p>
-{% endif %}
 {% if let Some(links) = rating %}
         <p class="rating">Was this a good pick? &#160; <a href="{{ links.loved_url }}">[ Loved it ]</a> &#160; <a href="{{ links.good_url }}">[ Good ]</a> &#160; <a href="{{ links.not_for_me_url }}">[ Not for me ]</a> &#160; <a href="{{ links.slop_url }}">[ AI slop ]</a> &#160;&#160;&#160; <a href="{{ read_online_url }}">Read online &#8599;</a></p>
 {% else %}