fix(pre-planting): 修复预种页面 5 个 UI 问题（纯前端，零后端改动）

=== 问题 1：流水明细合同按钮 500 错误 ===
文件: ledger_detail_page.dart
原因: 预种订单（PPL 前缀）无合同，但流水详情弹窗显示「查看合同/下载合同」按钮
修复: _showTransactionDetail 检测 refOrderId.startsWith('PPL')，
      预种订单传 showContractButtons: false，弹窗不渲染合同按钮区

=== 问题 2：流水备注显示英文 ===
文件: ledger_detail_page.dart
原因: 备注字段存储的是 'Plant payment (from frozen)'（后端写入，不改后端）
修复: _TransactionDetailSheet 展示备注时，若订单号以 PPL 开头则显示「预种」

=== 问题 3：预种明细订单金额单位错误 ===
文件: pre_planting_position_page.dart
修复: '${order.totalAmount.toInt()} USDT' → '${order.totalAmount.toInt()} 绿积分'

=== 问题 4：省市显示数字代码（如 44 · 4401）===
文件: pre_planting_position_page.dart / pre_planting_purchase_page.dart
原因: provinceName/cityName 为 null 时回退显示 provinceCode/cityCode
修复:
  - position 页：条件改为 provinceName != null && cityName != null，无中文名则不显示省市行
  - purchase 页：加载时不再 fallback 到代码；锁定显示无名称时显示「已锁定」；
    购买确认弹窗省市行无名称时显示「-」

=== 问题 5：「合并进度」改为「合成进度」===
文件: pre_planting_position_page.dart / pre_planting_purchase_page.dart
修复: 两处 Text('合并进度') → Text('合成进度')

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

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

@@ -345,9 +345,9 @@ class _PrePlantingPositionPageState
               ],
             ),
             const SizedBox(height: 16),
-            // 合并进度条
+            // 合成进度条
             const Text(
-              '合并进度',
+              '合成进度',
               style: TextStyle(
                 fontSize: 14,
                 fontFamily: 'Inter',
@@ -389,8 +389,8 @@ class _PrePlantingPositionPageState
                 ),
               ],
             ),
-            // 省市信息（如有）
+            // 省市信息（仅在有中文名称时显示）
-            if (pos.hasProvinceCity) ...[
+            if (pos.provinceName != null && pos.cityName != null) ...[
               const SizedBox(height: 12),
               Row(
                 children: [
@@ -401,7 +401,7 @@ class _PrePlantingPositionPageState
                   ),
                   const SizedBox(width: 4),
                   Text(
-                    '${pos.provinceName ?? pos.provinceCode} · ${pos.cityName ?? pos.cityCode}',
+                    '${pos.provinceName!} · ${pos.cityName!}',
                     style: const TextStyle(
                       fontSize: 13,
                       color: Color(0xFF745D43),
@@ -594,7 +594,7 @@ class _PrePlantingPositionPageState
               const SizedBox(width: 16),
               _buildInfoChip(
                 Icons.monetization_on_outlined,
-                '${order.totalAmount.toInt()} USDT',
+                '${order.totalAmount.toInt()} 绿积分',
               ),
             ],
           ),

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

@@ -166,12 +166,12 @@ class _PrePlantingPurchasePageState
         _pricePerPortion = pricingConfig.totalPortionPrice.toDouble();
         _isLoading = false;
 
-        // 续购时自动填入已保存的省市
+        // 续购时自动填入已保存的省市（名称不回退到代码，避免显示数字）
         if (position.hasProvinceCity) {
           _selectedProvinceCode = position.provinceCode;
-          _selectedProvinceName = position.provinceName ?? position.provinceCode;
+          _selectedProvinceName = position.provinceName;
           _selectedCityCode = position.cityCode;
-          _selectedCityName = position.cityName ?? position.cityCode;
+          _selectedCityName = position.cityName;
         }
 
         // 根据余额自动计算默认份数（默认 1 份）
@@ -445,7 +445,9 @@ class _PrePlantingPurchasePageState
             const SizedBox(height: 8),
             _buildDialogRow(
               '省市',
-              '${_selectedProvinceName ?? "-"} · ${_selectedCityName ?? "-"}',
+              _selectedProvinceName != null && _selectedCityName != null
+                  ? '$_selectedProvinceName · $_selectedCityName'
+                  : '-',
             ),
             if (_position != null) ...[
               const Divider(height: 24, color: Color(0x338B5A2B)),
@@ -884,7 +886,7 @@ class _PrePlantingPurchasePageState
             mainAxisAlignment: MainAxisAlignment.spaceBetween,
             children: [
               const Text(
-                '合并进度',
+                '合成进度',
                 style: TextStyle(
                   fontSize: 16,
                   fontFamily: 'Inter',
@@ -1037,7 +1039,9 @@ class _PrePlantingPurchasePageState
                 children: [
                   Text(
                     _hasSelectedProvinceCity
+                        ? (_selectedProvinceName != null && _selectedCityName != null
                             ? '$_selectedProvinceName · $_selectedCityName'
+                            : '已锁定')
                         : '点击选择省份和城市',
                     style: TextStyle(
                       fontSize: 16,

frontend/mobile-app/lib/features/trading/presentation/pages/ledger_detail_page.dart

@@ -1116,14 +1116,18 @@ class _LedgerDetailPageState extends ConsumerState<LedgerDetailPage>
   Future<void> _showTransactionDetail(LedgerEntry entry) async {
     if (entry.refOrderId == null) return;
 
+    // 预种订单（PPL 前缀）没有合同，不显示合同按钮
+    final bool isPrePlanting = entry.refOrderId!.startsWith('PPL');
+
     showModalBottomSheet(
       context: context,
       isScrollControlled: true,
       backgroundColor: Colors.transparent,
       builder: (context) => _TransactionDetailSheet(
         entry: entry,
-        onViewContract: () => _viewContractPdf(entry.refOrderId!),
+        showContractButtons: !isPrePlanting,
-        onDownloadContract: () => _downloadContractPdf(entry.refOrderId!),
+        onViewContract: isPrePlanting ? null : () => _viewContractPdf(entry.refOrderId!),
+        onDownloadContract: isPrePlanting ? null : () => _downloadContractPdf(entry.refOrderId!),
       ),
     );
   }
@@ -1231,13 +1235,15 @@ class _LedgerDetailPageState extends ConsumerState<LedgerDetailPage>
 /// 交易详情底部弹窗
 class _TransactionDetailSheet extends StatelessWidget {
   final LedgerEntry entry;
-  final VoidCallback onViewContract;
+  final VoidCallback? onViewContract;
-  final VoidCallback onDownloadContract;
+  final VoidCallback? onDownloadContract;
+  final bool showContractButtons;
 
   const _TransactionDetailSheet({
     required this.entry,
-    required this.onViewContract,
+    this.onViewContract,
-    required this.onDownloadContract,
+    this.onDownloadContract,
+    this.showContractButtons = true,
   });
 
   @override
@@ -1326,16 +1332,17 @@ class _TransactionDetailSheet extends StatelessWidget {
                     _buildDetailRow('交易后余额', '${_formatAmount(entry.balanceAfter!)} 绿积分'),
                   _buildDetailRow('交易时间', _formatDateTime(entry.createdAt)),
                   if (entry.memo != null && entry.memo!.isNotEmpty)
-                    _buildDetailRow('备注', entry.memo!),
+                    _buildDetailRow('备注',
+                        entry.refOrderId?.startsWith('PPL') == true ? '预种' : entry.memo!),
                 ],
               ),
             ),
-            // 分隔线
+            // 合同操作按钮（仅认种支付显示，预种无合同）
+            if (showContractButtons) ...[
               Container(
                 height: 1,
                 color: const Color(0x1A8B5A2B),
               ),
-            // 操作按钮
               Padding(
                 padding: const EdgeInsets.all(20),
                 child: Row(
@@ -1344,7 +1351,7 @@ class _TransactionDetailSheet extends StatelessWidget {
                       child: OutlinedButton.icon(
                         onPressed: () {
                           Navigator.of(context).pop();
-                        onViewContract();
+                          onViewContract?.call();
                         },
                         icon: const Icon(Icons.visibility_outlined, size: 18),
                         label: const Text('查看合同'),
@@ -1363,7 +1370,7 @@ class _TransactionDetailSheet extends StatelessWidget {
                       child: ElevatedButton.icon(
                         onPressed: () {
                           Navigator.of(context).pop();
-                        onDownloadContract();
+                          onDownloadContract?.call();
                         },
                         icon: const Icon(Icons.download_outlined, size: 18),
                         label: const Text('下载合同'),
@@ -1381,6 +1388,7 @@ class _TransactionDetailSheet extends StatelessWidget {
                 ),
               ),
             ],
+          ],
         ),
       ),
     );