feat(admin-web): 仪表板添加预种待合并/已合并统计卡片

在网络因子/加速因子下方新增一行：
- 预种待合并: 显示全网 pendingMergePortions（份）
- 预种已合并: 显示全网 totalTreesMerged（棵）

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

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

@@ -19,6 +19,7 @@ import {
   usePlantingStats,
   usePlantingTrendForDashboard,
   useHotWalletBalance,
+  usePrePlantingStats,
 } from '@/hooks';
 import type { DashboardPeriod } from '@/types';
 import styles from './dashboard.module.scss';
@@ -100,6 +101,12 @@ export default function DashboardPage() {
     isLoading: hotWalletLoading,
   } = useHotWalletBalance();
 
+  // 预种统计（待合并/已合并）
+  const {
+    data: prePlantingStats,
+    isLoading: prePlantingStatsLoading,
+  } = usePrePlantingStats();
+
   // [2026-01-06] 基于 planting-service 数据构建统计卡片数据
   const statsCards = plantingStatsData ? [
     {
@@ -219,6 +226,36 @@ 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}>