feat(records): 训练趋势图表 + 列表时长改 MM:SS

- 新增 trend-chart 柱状图组件(CSS,近7天/近6月切换)
- records 页加训练趋势卡片(统计卡片后)
- 训练记录列表时长从秒数改为 MM:SS 显示

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

components/trend-chart/trend-chart.wxml

@@ -0,0 +1,12 @@
+<view class="trend-chart">
+  <view class="trend-bars">
+    <view class="trend-bar-col" wx:for="{{bars}}" wx:key="label">
+      <view class="trend-bar {{item.value === 0 ? 'zero' : ''}} {{item.highlight ? 'highlight' : ''}}" style="height: {{item.percent}}%;">
+        <text class="trend-bar-value" wx:if="{{item.value > 0}}">{{item.valueText}}</text>
+      </view>
+    </view>
+  </view>
+  <view class="trend-labels">
+    <text class="trend-bar-label {{item.highlight ? 'highlight' : ''}}" wx:for="{{bars}}" wx:key="label">{{item.label}}</text>
+  </view>
+</view>