fix(detailedReport): 卡片无数据时隐藏整卡，wx:if 统一写 block 上

- 删除多余的 isEightElectrode 字段
- 各指标卡片 rows 为空时不渲染标题
- wx:if 统一移到 block 上，符合 wxml 规范

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

miniprogram/pages/detailedReport/detailedReport.ts

@@ -189,7 +189,6 @@ Page({
         weightControl: { title: '体重管控', rows: [] } as MetricCard,
 
         // 以下卡片为 8 电极专属
-        isEightElectrode: false,
         cellWater: { title: '细胞液分析', rows: [] } as MetricCard,
         advancedComposition: { title: '进阶成分', rows: [] } as MetricCard,
         bodyFat: { title: '躯干/四肢脂肪', rows: [] } as BodyPartsCard,
@@ -347,7 +346,6 @@ Page({
             fatAnalysis,
             physique,
             weightControl,
-            isEightElectrode: isEight,
             cellWater,
             advancedComposition,
             bodyFat,