Show matched interests as a tag row instead of a callout

With the why line gone the accent-bar callout held nothing but "Matches: a · b",
which no longer earned its quoting. Every surface now puts one row directly
under the rubric: a small-caps "Matches" label and one pill chip per interest.
On the web that is one `.interest-chip` component (admins still get links to
the interest's article filter); the EPUB gets `.matches`/`.interest` rules in
both stylesheets, and `Understanding::interests_line` goes.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ESJbbzQ1b8fs5AA65tKw2q

src/epub/templates/chapter.xhtml

@@ -11,11 +11,7 @@
         <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 !understanding.interests.is_empty() %}
-        <div class="why">
-{% if !understanding.interests.is_empty() %}
-          <p class="why-matches">Matches: {{ understanding.interests_line() }}</p>
-{% endif %}
-        </div>
+        <p class="matches"><span class="kicker">Matches</span>{% for interest in understanding.interests %} <span class="interest">{{ interest.name }}</span>{% endfor %}</p>
 {% endif %}
 {% if let Some(text) = summary %}
         <p class="summary">{{ text }}</p>