feat(data): 体重差值按 weightDiff/weightTrend 动态渲染并区分增减颜色

- 差值图标与数值改用后端 weightDiff/weightTrend
- 首次测量/持平不显示差值块
- 增加红色、减少绿色

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

miniprogram/pages/data/data.less

@@ -325,6 +325,14 @@
 								height: 26rpx;
 								line-height: 26rpx;
 							}
+
+							&.diff-up {
+								background-color: #FEF0F0;
+
+								> view:nth-of-type(2) {
+									color: #F24439;
+								}
+							}
 						}
 
 						&.arrow::after {

miniprogram/pages/data/data.ts

@@ -38,6 +38,10 @@ interface MeasureRecord {
     weight: number
     bmi: number
     fatRate: number
+    /** 相比上次体重差值绝对值(kg)，首次测量为 null */
+    weightDiff: number | null
+    /** 变化方向：1增加 -1减少 0持平 null首次 */
+    weightTrend: number | null
 }
 
 /** GET /weighingScale/v3/getMeasureHistoryPage 返回结构 */
@@ -150,6 +154,8 @@ Page({
                     weight: r.weight ?? 0,
                     bmi: r.bmi ?? 0,
                     fatRate: r.fatRate ?? 0,
+                    weightDiff: r.weightDiff == null ? null : Math.abs(r.weightDiff),
+                    weightTrend: r.weightTrend ?? null,
                 }))
                 const total = page.total ?? 0
 
@@ -191,6 +197,8 @@ Page({
                     weight: r.weight ?? 0,
                     bmi: r.bmi ?? 0,
                     fatRate: r.fatRate ?? 0,
+                    weightDiff: r.weightDiff == null ? null : Math.abs(r.weightDiff),
+                    weightTrend: r.weightTrend ?? null,
                 }))
                 const allRecords = [...this.data.records, ...newRecords]
                 this.setData({

miniprogram/pages/data/data.wxml

@@ -73,12 +73,14 @@
 								<view class="list-examTime">{{ item.examTime }}</view>
 								<view class="list-weight arrow">
 									<view>{{ item.weight }}<text>kg</text></view>
-									<view>
-										<view>
-											<image src="/images/data/sub.png" mode="aspectFit" />
+									<block wx:if="{{ item.weightTrend === 1 || item.weightTrend === -1 }}">
+										<view class="{{ item.weightTrend === 1 ? 'diff-up' : '' }}">
+											<view>
+												<image src="{{ item.weightTrend === 1 ? '/images/data/add.png' : '/images/data/sub.png' }}" mode="aspectFit" />
+											</view>
+											<view>{{ item.weightDiff }}</view>
 										</view>
-										<view>0.3</view>
-									</view>
+									</block>
 								</view>
 								<view class="list-bmi">
 									<view>