feat: add AI disclaimer at bottom of health coach chat page

cfc-frontend/pages/ai/chat.vue

@@ -148,6 +148,7 @@
         <text class="send-icon">➤</text>
       </view>
     </view>
+    <view class="chat-disclaimer">本服务为AI生成内容，结果仅供参考</view>
   </view>
 </template>
 
@@ -884,4 +885,11 @@ export default {
   color: #6366F1;
   font-weight: 500;
 }
+.chat-disclaimer {
+  text-align: center;
+  font-size: 22rpx;
+  color: #999;
+  padding: 16rpx 0 20rpx;
+  background: #f5f5f5;
+}
 </style>