fix: 滑动卡片指示器联动 — _cardIdx从computed迁移到data独立管理

根因: _cardIdx存在computed lane对象中, computed重新计算时重置为0
修复: cardIndices{}独立data管理, keyed by lane._key
      新增watch product重置 + getCardIdx/setCardIdx方法

track-uniapp/src/pages/scan/components/TaskSwipeCards.vue

@@ -6,7 +6,7 @@
       <view class="ss-title-group">
         <text class="ss-title">{{ lanes[currentLane].label }}</text>
         <text class="ss-step-hint">
-          步骤 {{ lanes[currentLane]._cardIdx + 1 }}/{{ lanes[currentLane].cards.length }}
+          步骤 {{ getCardIdx(lanes[currentLane]._key) + 1 }}/{{ lanes[currentLane].cards.length }}
           <text v-if="lanes.length > 1"> · ← 左右滑切换分支 →</text>
         </text>
       </view>
@@ -20,7 +20,7 @@
       :style="{ height: swiperHeight + 'px' }" duration="250">
       <swiper-item v-for="(lane, li) in lanes" :key="lane._key">
         <!-- 🚀 垂直滑动：当前分支的时间线 -->
-        <swiper class="ss-swiper-v" :current="lane._cardIdx" @change="onCardSwipe($event, li)"
+        <swiper class="ss-swiper-v" :current="getCardIdx(lane._key)" @change="onCardSwipe($event, li)"
           duration="200" vertical :style="{ height: swiperHeight + 'px' }">
           <swiper-item v-for="(card, ci) in lane.cards" :key="card._key">
             <view class="ss-card-wrapper">
@@ -85,7 +85,7 @@
       </view>
       <view class="ss-dots">
         <view v-for="(c, i) in lanes[currentLane].cards" :key="'d'+i"
-          :class="['ss-dot', i === lanes[currentLane]._cardIdx ? 'ss-dot-active' : '', c._isMain ? 'ss-dot-main' : '']">
+          :class="['ss-dot', i === getCardIdx(lanes[currentLane]._key) ? 'ss-dot-active' : '', c._isMain ? 'ss-dot-main' : '']">
           <text class="ss-dot-label">{{ i + 1 }}</text>
         </view>
       </view>
@@ -104,9 +104,17 @@ export default {
   data() {
     return {
       currentLane: 0,
+      cardIndices: {},  // { laneKey: currentCardIndex } — 独立管理避免computed重置
       swiperHeight: 600,
     };
   },
+  watch: {
+    // product 变化时重置所有滑动位置
+    product: {
+      immediate: true,
+      handler() { this.cardIndices = {}; },
+    },
+  },
   computed: {
     branchLabelMap() {
       const map = {};
@@ -133,7 +141,7 @@ export default {
       const result = [];
       if (!this.product || !this.product.task_tree) return result;
 
-      const mainLane = { _key: 'main', label: '主分支', cards: [], _cardIdx: 0 };
+      const mainLane = { _key: 'main', label: '主分支', cards: [] };
 
       const sortTasks = (tasks) => {
         if (!tasks) return [];
@@ -160,7 +168,7 @@ export default {
             const spawns = t.child_tasks.filter(c => c.task_type === 'SPAWN');
             for (const sc of spawns) {
               const blabel = (this.branchLabelMap && this.branchLabelMap[sc.id]) || '协助分支';
-              const branchLane = { _key: 'branch_' + sc.id, label: blabel, cards: [], _cardIdx: 0 };
+              const branchLane = { _key: 'branch_' + sc.id, label: blabel, cards: [] };
               result.push(branchLane);      // 先占坑：父分支排在前面
               followMain([sc], branchLane); // 再递归：孙子分支自然排在后面
             }
@@ -181,10 +189,13 @@ export default {
   },
   methods: {
     formatUserName,
+    getCardIdx(laneKey) { return this.cardIndices[laneKey] || 0; },
+    setCardIdx(laneKey, idx) { this.$set(this.cardIndices, laneKey, idx); },
     onLaneSwipe(e) { this.currentLane = e.detail.current; },
     onCardSwipe(e, laneIdx) {
-      if (this.lanes[laneIdx]) {
-        this.$set(this.lanes[laneIdx], '_cardIdx', e.detail.current);
+      const lane = this.lanes[laneIdx];
+      if (lane) {
+        this.setCardIdx(lane._key, e.detail.current);
       }
     },
     taskCardClass(t) {