fix: 近30日趋势显示30天数据点而非4周

- 新增getXLabels30()函数，生成近30天的日期标签
- AQI柱状图近30日改为30根柱子对应30天（替代原来的4周标签）
- 普通指标折线图近30日显示30个数据点+30天日期标签

employee-app/health-monitor/environment/device-detail.html

@@ -367,6 +367,14 @@ function getXLabels7() {
   }
   return labels;
 }
+function getXLabels30() {
+  var labels = [], now = new Date(2026, 5, 4);
+  for (var i = 29; i >= 0; i--) {
+    var d = new Date(now); d.setDate(d.getDate() - i);
+    labels.push((d.getMonth()+1) + '/' + d.getDate());
+  }
+  return labels;
+}
 
 /* X 坐标计算 */
 function calcXPositions(count) {
@@ -460,14 +468,13 @@ function renderTrend(metricName, period) {
 
   // AQI 非 24h → 柱状堆积图
   if (cfg.isAQI && period !== '24h') {
-    var labels = period === '7d' ? getXLabels7() : Array.from({length:4}, function(_, i) { return '第' + (i+1) + '周'; });
+    var labels = period === '7d' ? getXLabels7() : getXLabels30();
     return renderAQIBarChart(timeData, labels);
   }
 
   var points = timeData.points;
   var n = points.length;
-  var labels = cfg.isAQI ? (period === '24h' ? xLabels24 : getXLabels7()) : (period === '24h' ? xLabels24 : getXLabels7());
-  if (period === '30d' && n === 30) labels = (function() { var l = [], now = new Date(2026,5,4); for (var i = 29; i >= 0; i--) { var d = new Date(now); d.setDate(d.getDate() - i); l.push((d.getMonth()+1) + '/' + d.getDate()); } return l; })();
+  var labels = period === '24h' ? xLabels24 : (period === '7d' ? getXLabels7() : getXLabels30());
 
   var xPositions = calcXPositions(n);
   var yMax = cfg.yMax;