fix(planting-service+app): 合并列表补充 totalPortions，前端显示实际份数而非订单数

- getMerges 批量查来源订单 portionCount，按合并分组求和后返回 totalPortions
- 预种明细合并卡片改用 totalPortions 显示份数，fallback 才用订单数

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

backend/services/planting-service/src/pre-planting/application/services/pre-planting-application.service.ts

@@ -368,6 +368,7 @@ export class PrePlantingApplicationService {
   async getMerges(userId: bigint): Promise<{
     mergeNo: string;
     sourceOrderNos: string[];
+    totalPortions: number;
     treeCount: number;
     contractStatus: string;
     contractSignedAt: Date | null;
@@ -376,9 +377,20 @@ export class PrePlantingApplicationService {
   }[]> {
     return this.prisma.$transaction(async (tx) => {
       const merges = await this.mergeRepo.findByUserId(tx, userId);
+      if (merges.length === 0) return [];
+
+      // 批量查询所有合并的来源订单份数
+      const allOrderNos = merges.flatMap((m) => m.sourceOrderNos);
+      const orderRecords = await tx.prePlantingOrder.findMany({
+        where: { orderNo: { in: allOrderNos } },
+        select: { orderNo: true, portionCount: true },
+      });
+      const portionByOrderNo = new Map(orderRecords.map((o) => [o.orderNo, o.portionCount]));
+
       return merges.map((m) => ({
         mergeNo: m.mergeNo,
         sourceOrderNos: m.sourceOrderNos,
+        totalPortions: m.sourceOrderNos.reduce((sum, no) => sum + (portionByOrderNo.get(no) ?? 1), 0),
         treeCount: m.treeCount,
         contractStatus: m.contractStatus,
         contractSignedAt: m.contractSignedAt,

frontend/mobile-app/lib/features/pre_planting/presentation/pages/pre_planting_position_page.dart

@@ -669,7 +669,7 @@ class _PrePlantingPositionPageState
                 const SizedBox(width: 16),
                 _buildInfoChip(
                   Icons.layers_outlined,
-                  '${merge.sourceOrderNos.length} 份合并',
+                  '${merge.totalPortions > 0 ? merge.totalPortions : merge.sourceOrderNos.length} 份合并',
                 ),
               ],
             ),