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/in_this_issue.xhtml

@@ -14,11 +14,7 @@
           <p class="rubric">{% if let Some(kicker) = entry.understanding.kicker %}<span class="kicker">{{ kicker }}</span>{% if let Some(topics) = entry.understanding.topics %} &#160; {{ topics }}{% endif %}{% else %}{% if let Some(topics) = entry.understanding.topics %}{{ topics }}{% endif %}{% endif %}</p>
 {% endif %}
 {% if !entry.understanding.interests.is_empty() %}
-          <div class="index-why">
-{% if !entry.understanding.interests.is_empty() %}
-            <p class="why-matches">Matches: {{ entry.understanding.interests_line() }}</p>
-{% endif %}
-          </div>
+          <p class="matches"><span class="kicker">Matches</span>{% for interest in entry.understanding.interests %} <span class="interest">{{ interest.name }}</span>{% endfor %}</p>
 {% endif %}
 {% if !entry.summary.is_empty() %}
           <p class="index-summary">{{ entry.summary }}</p>