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 %}

app/templates/postcard_form.html

@@ -33,6 +33,9 @@
         <input type="date" name="receive_time" id="input-receive" value="{{ postcard.receive_time.strftime('%Y-%m-%d') if postcard and postcard.receive_time else '' }}">
     </div>
 
+    <label>备注</label>
+    <textarea name="notes" rows="3" placeholder="可选备注信息">{{ postcard.notes if postcard else '' }}</textarea>
+
     <div class="form-actions">
         <button type="submit" class="btn btn-primary">保存</button>
         <a href="/profiles/{{ profile.id }}/postcards" class="btn">取消</a>

app/templates/postcards.html

@@ -44,6 +44,7 @@
             <span>{{ pc.country|flag }} {{ pc.country or '-' }}</span>
             <span>→ {{ pc.recipient_name or '-' }}</span>
         </div>
+        {% if pc.notes %}<span class="postcard-row-notes">{{ pc.notes[:50] }}{% if pc.notes|length > 50 %}…{% endif %}</span>{% endif %}
         <span class="badge badge-{{ pc.status }}">{{ {'sent':'已寄出','delivered':'已送达'}.get(pc.status) }}</span>
         <span class="postcard-row-date">
             {% if pc.send_time %}{{ pc.send_time.strftime('%Y-%m-%d') }}寄出{% endif %}
@@ -80,6 +81,7 @@
         <div class="postcard-row-detail">
             <span>← {{ pc.sender_name or '-' }}</span>
         </div>
+        {% if pc.notes %}<span class="postcard-row-notes">{{ pc.notes[:50] }}{% if pc.notes|length > 50 %}…{% endif %}</span>{% endif %}
         {% if pc.receive_time %}<span class="postcard-row-date">{{ pc.receive_time.strftime('%Y-%m-%d') }}收到</span>{% endif %}
     </div>
 </a>