feat(postcards): add notes field to postcards with edit, detail, and truncated list display

app/templates/postcard_detail.html

@@ -61,6 +61,9 @@
             {% endif %}
             <dt>所属 Profile</dt><dd>{{ postcard.profile.nickname }}</dd>
         </dl>
+        {% if postcard.notes %}
+        <div class="detail-notes">{{ postcard.notes }}</div>
+        {% endif %}
     </div>
 </div>
 {% endblock %}