fix(admin-web): 仪表板预种统计改为方块卡片样式

- 预种待合并/已合并从深色条形卡片改为与认种统计一致的 StatCard
- 统计网格从 4 列调整为 3 列（3+3 布局更工整）
- 骨架屏占位从 4 个调整为 6 个

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/admin-web/src/app/(dashboard)/dashboard/dashboard.module.scss

@@ -8,7 +8,7 @@
 
   &__stats {
     display: grid;
-    grid-template-columns: repeat(4, 1fr);
+    grid-template-columns: repeat(3, 1fr);
     gap: $spacing-lg;
 
     @include respond-below(xl) {

frontend/admin-web/src/app/(dashboard)/dashboard/page.tsx

@@ -137,6 +137,20 @@ export default function DashboardPage() {
       change: { value: 0, trend: 'up' as const },
       color: '#8b5cf6',
     },
+    {
+      title: '预种待合并',
+      value: prePlantingStats?.pendingMergePortions ?? 0,
+      suffix: '份',
+      change: { value: 0, trend: 'up' as const },
+      color: '#ef4444',
+    },
+    {
+      title: '预种已合并',
+      value: prePlantingStats?.totalTreesMerged ?? 0,
+      suffix: '棵',
+      change: { value: 0, trend: 'up' as const },
+      color: '#06b6d4',
+    },
   ] : [];
 
   const headerActions = (
@@ -165,7 +179,7 @@ export default function DashboardPage() {
           {statsLoading ? (
             // 加载状态显示骨架屏
             <>
-              {[1, 2, 3, 4].map((i) => (
+              {[1, 2, 3, 4, 5, 6].map((i) => (
                 <StatCardSkeleton key={i} />
               ))}
             </>
@@ -226,36 +240,6 @@ export default function DashboardPage() {
           </div>
         </div>
 
-        {/* 预种统计区域 */}
-        <div className={styles.dashboard__walletBalance}>
-          <div className={styles.dashboard__walletCard}>
-            <div className={styles.dashboard__walletLabel}>预种待合并</div>
-            <div className={styles.dashboard__walletValue}>
-              {prePlantingStatsLoading ? (
-                <span className={styles.dashboard__walletLoading}>加载中...</span>
-              ) : (
-                <span className={styles.dashboard__walletAmount}>
-                  {(prePlantingStats?.pendingMergePortions ?? 0).toLocaleString()}
-                  <span style={{ fontSize: '0.5em', marginLeft: 4, opacity: 0.7 }}>份</span>
-                </span>
-              )}
-            </div>
-          </div>
-          <div className={styles.dashboard__walletCard}>
-            <div className={styles.dashboard__walletLabel}>预种已合并</div>
-            <div className={styles.dashboard__walletValue}>
-              {prePlantingStatsLoading ? (
-                <span className={styles.dashboard__walletLoading}>加载中...</span>
-              ) : (
-                <span className={styles.dashboard__walletAmount}>
-                  {(prePlantingStats?.totalTreesMerged ?? 0).toLocaleString()}
-                  <span style={{ fontSize: '0.5em', marginLeft: 4, opacity: 0.7 }}>棵</span>
-                </span>
-              )}
-            </div>
-          </div>
-        </div>
-
         {/* 图表区 - [2026-01-06] 使用 planting-service 数据 */}
         <div className={styles.dashboard__charts}>
           <div className={styles.dashboard__mainChart}>