fix(mobile-app): 待签署合同页文案改为"10份预种份额已合并为1棵树"

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

frontend/mobile-app/lib/features/contract_signing/presentation/pages/pending_contracts_page.dart

@@ -417,7 +417,7 @@ class _PendingContractsPageState extends ConsumerState<PendingContractsPage> {
                 color: const Color(0xFFE8F5E9),
                 icon: Icons.park_outlined,
                 iconColor: const Color(0xFF4CAF50),
-                text: '${merge.sourceOrderNos.length} 笔预种订单已合并为 ${merge.treeCount} 棵树，请签署合同以开启挖矿',
+                text: '10 份预种份额已合并为 ${merge.treeCount} 棵树，请签署合同以开启挖矿',
                 textColor: const Color(0xFF2E7D32),
               ),
               const SizedBox(height: 12),