调整图表布局 - 将用户转化率图移到日活用户趋势图下方，形成垂直布局

demo/frontend/src/views/Home.vue

@@ -99,7 +99,7 @@
       <!-- 图表区域 -->
       <section class="charts-section">
         <!-- 日活用户趋势图 -->
-        <div class="chart-card">
+        <div class="chart-card full-width">
           <div class="chart-header">
             <h3>日活用户趋势</h3>
             <div class="year-selector">
@@ -179,7 +179,7 @@
         </div>
 
         <!-- 用户转化率图 -->
-        <div class="chart-card">
+        <div class="chart-card full-width">
           <div class="chart-header">
             <h3>用户转化率</h3>
             <div class="year-selector">
@@ -542,11 +542,15 @@ onMounted(() => {
 /* 图表区域 */
 .charts-section {
   padding: 0 24px 24px;
-  display: grid;
-  grid-template-columns: 2fr 1fr;
+  display: flex;
+  flex-direction: column;
   gap: 24px;
 }
 
+.chart-card.full-width {
+  width: 100%;
+}
+
 .chart-card {
   background: white;
   border-radius: 12px;
@@ -732,10 +736,6 @@ onMounted(() => {
 
 /* 响应式设计 */
 @media (max-width: 1024px) {
-  .charts-section {
-    grid-template-columns: 1fr;
-  }
-  
   .kpi-section {
     grid-template-columns: 1fr;
   }