Add conference count display to conference list sections

- Show count of conferences in each section (Current/Future/Past)
- Include proper pluralization (1 conference vs N conferences)
- Use Jinja2 template logic for count calculation and display

Fixes #195

templates/conference_list.html

@@ -26,7 +26,16 @@
 
 {% macro section(heading, item_list, badge) %}
   {% if item_list %}
-    <div class="heading"><h2>{{ heading }}</h2></div>
+    <div class="heading">
+
+      <h2>{{ heading }}</h2>
+
+      <p>
+        {% set item_count = item_list|length %}
+        {% if item_count == 1 %}{{ item_count }} conference{% else %}{{ item_count }} conferences{% endif %}
+      </p>
+    </div>
+
     {% for item in item_list %}
       {{ conference_row(item, badge) }}
       <div class="grid-item">