Phase 4: add container-nav/cards fragment handlers, use market fragment

Events provides container-nav (calendar entries + links) and
container-cards (batch entries for blog listing) as fragments.
Day and entry routes fetch market container-nav via fragment instead
of widget registry.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/fragments/container_nav_entries.html

@@ -0,0 +1,28 @@
+{# Calendar entries nav — served as fragment from events app #}
+{% for entry in entries %}
+  {% set _entry_path = '/' + post_slug + '/calendars/' + entry.calendar_slug + '/' + entry.start_at.year|string + '/' + entry.start_at.month|string + '/' + entry.start_at.day|string + '/entries/' + entry.id|string + '/' %}
+  <a
+    href="{{ events_url(_entry_path) }}"
+    class="{{styles.nav_button_less_pad}}"
+  >
+    <div class="w-8 h-8 rounded bg-stone-200 flex-shrink-0"></div>
+    <div class="flex-1 min-w-0">
+      <div class="font-medium truncate">{{ entry.name }}</div>
+      <div class="text-xs text-stone-600 truncate">
+        {{ entry.start_at.strftime('%b %d, %Y at %H:%M') }}
+        {% if entry.end_at %} – {{ entry.end_at.strftime('%H:%M') }}{% endif %}
+      </div>
+    </div>
+  </a>
+{% endfor %}
+
+{# Infinite scroll sentinel — URL points back to the consumer app #}
+{% if has_more and paginate_url_base %}
+  <div id="entries-load-sentinel-{{ page }}"
+       hx-get="{{ paginate_url_base }}?page={{ page + 1 }}"
+       hx-trigger="intersect once"
+       hx-swap="beforebegin"
+       _="on htmx:afterRequest trigger scroll on #associated-entries-container"
+       class="flex-shrink-0 w-1">
+  </div>
+{% endif %}