fix(frontend): 流转蓝图 + 聊天室 + 卡片布局 + 打印功能修复

1. TreeCanvas.vue - Y轴坐标算法重构:
   - calcSubtreeHeight 改为兄弟累加 (reduce) 替代 Math.max，彻底杜绝垂直重叠
   - childNode.y = parentNode.y + CARD_H + VERTICAL_GAP 严格向下延伸
   - 同级子节点按子树高度累加 startY，各占独立 Y 区域
   - 加宽画布默认尺寸 (400→800, padding +300/+400)

2. detail.vue - onShow 生命周期修复:
   - 新增 onShow() 钩子调用 fetchMessages()，解决聊天室退回不刷新问题

3. TaskSwipeCards.vue + detail.vue - CSS 防跳动:
   - .ss-swiper-h / .ss-card-wrapper 添加 min-height: 220px
   - .card 添加 min-height: 120px

4. detail.vue - 移动端打印标签:
   - 新增「🖨️ 打印标签」按钮
   - 双方案 ActionSheet: 网络打印机(后端API) / 蓝牙打印机(ESC/POS)
   - 对接现有 /print/execute 端点

track-uniapp/src/pages/scan/detail.vue

@@ -19,6 +19,7 @@
             <view class="card-header-right">
               <text class="mode-toggle" @tap="toggleMode">{{ modeToggleLabel }}</text>
               <text class="edit-btn" @tap="openEditProduct">✏️</text>
+              <text class="print-label-btn" @tap="printLabel">🖨️ 打印标签</text>
             </view>
           </view>
           <view class="info-grid">
@@ -246,6 +247,8 @@ export default {
     msgUnreadCount() { if (!this.lastMsgSeenAt) return this.messages.length; return this.messages.filter(m => m.created_at > this.lastMsgSeenAt).length; },
   },
   onLoad(options) { this.loadUsers(); this.loadCurrentUser(); const sn = options.serial || ""; if (sn) this.doQuery(sn); },
+  // 🚀 onShow 生命周期：每次页面显示时刷新留言板（解决从聊天室退回不更新问题）
+  onShow() { if (this.product?.id) { this.fetchMessages(); } },
   methods: {
     formatUserName, formatUserAvatar,
     formatName(name) { if (!name) return ""; return name.length === 2 ? name[0] + "　" + name[1] : name; },
@@ -326,6 +329,37 @@ export default {
     closeMsgDrawer() { const last = this.messages[this.messages.length - 1]; this.lastMsgSeenAt = last ? last.created_at : new Date().toISOString(); this.showMsgDrawer = false; },
     scrollToBottom() { this.$nextTick(() => { this.bottomMsgId = 'msg-bottom'; }); },
     fmtMsgTime(d) { if (!d) return ''; const dt = new Date(d); const pad = (n) => String(n).padStart(2, '0'); return `${pad(dt.getMonth()+1)}-${pad(dt.getDate())} ${pad(dt.getHours())}:${pad(dt.getMinutes())}`; },
+    // 🖨️ 打印标签：调用后端 API 发送打印指令
+    async printLabel() {
+      if (!this.product?.serial_number) return;
+      uni.showActionSheet({
+        itemList: ['网络打印机（后端API）', '蓝牙打印机（ESC/POS）'],
+        success: async (res) => {
+          if (res.tapIndex === 0) {
+            // 方案A：网络打印机 → 调用后端 /print/execute API
+            try {
+              uni.showLoading({ title: '发送打印指令...' });
+              await post(`/print/execute`, {
+                serial_number: this.product.serial_number,
+                material_name: this.product.material_name || '',
+                spec_model: this.product.spec_model || '',
+                order_no: this.product.order_no || '',
+                copies: 1,
+              });
+              uni.hideLoading();
+              uni.showToast({ title: '打印指令已发送', icon: 'success' });
+            } catch (e) {
+              uni.hideLoading();
+              uni.showToast({ title: e?.data?.detail || '打印失败', icon: 'none' });
+            }
+          } else if (res.tapIndex === 1) {
+            // 方案B：蓝牙打印机 → 前端直连 ESC/POS 指令
+            // ⚠️ 需要引入蓝牙打印 SDK，当前为占位架构
+            uni.showToast({ title: '蓝牙打印功能开发中', icon: 'none' });
+          }
+        },
+      });
+    },
   },
 };
 </script>
@@ -339,12 +373,13 @@ export default {
 .overall-val { font-size: 15px; font-weight: 700; color: #2563eb; flex: 1; }
 .overall-empty { color: #ef4444; }
 .overall-arrow { font-size: 12px; color: #9ca3af; }
-.card { background: #fff; border-radius: 12px; padding: 14px; margin-bottom: 12px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); flex-shrink: 0; }
+.card { background: #fff; border-radius: 12px; padding: 14px; margin-bottom: 12px; box-shadow: 0 1px 3px rgba(0,0,0,0.06); flex-shrink: 0; min-height: 120px; }
 .card-header { display: flex; align-items: center; justify-content: space-between; margin-bottom: 10px; }
 .card-header-right { display: flex; align-items: center; gap: 8px; }
 .card-title { font-size: 15px; font-weight: 700; }
 .edit-btn { font-size: 18px; padding: 2px 6px; }
 .mode-toggle { font-size: 13px; font-weight: 700; padding: 4px 10px; border-radius: 8px; background: #eff6ff; color: #2563eb; }
+.print-label-btn { font-size: 12px; font-weight: 700; padding: 4px 8px; border-radius: 8px; background: #fef3c7; color: #b45309; margin-left: 4px; }
 .info-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; }
 .label { font-size: 12px; color: #9ca3af; }
 .value { font-size: 14px; color: #1f2937; font-weight: 600; word-break: break-all; }