feat(client): 录单表单优化 + 可搜索下拉支持新建 + 日期选择器组件

新增 DatePickerField 日期选择器与 date_util；可搜索下拉 SearchableOptionField
支持内联新建选项；入库/出库录单表单、商品页、财务页、app_shell 导航相应调整。

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

client/lib/models/shop.dart

@@ -7,6 +7,8 @@ class ShopInfo {
   final String managerName;
   final String logoUrl;
   final String wechatId;
+  // 店级动态配置（后端 shops.custom_fields JSON），存录入默认值等轻量配置
+  final Map<String, dynamic> customFields;
 
   const ShopInfo({
     required this.id,
@@ -17,8 +19,24 @@ class ShopInfo {
     required this.managerName,
     this.logoUrl = '',
     this.wechatId = '',
+    this.customFields = const {},
   });
 
+  /// 入库录入默认商品名称选项 id（未配置返回 null）。
+  int? get defaultNameId => _asInt(customFields['default_name_id']);
+
+  /// 入库录入默认系列选项 id（未配置返回 null）。
+  int? get defaultSeriesId => _asInt(customFields['default_series_id']);
+
+  /// 入库录入默认规格选项 id（未配置返回 null）。
+  int? get defaultSpecId => _asInt(customFields['default_spec_id']);
+
+  static int? _asInt(dynamic v) {
+    if (v == null) return null;
+    if (v is num) return v.toInt();
+    return int.tryParse(v.toString());
+  }
+
   factory ShopInfo.fromJson(Map<String, dynamic> json) => ShopInfo(
         id: (json['id'] as num).toInt(),
         code: json['code'] as String? ?? '',
@@ -28,5 +46,8 @@ class ShopInfo {
         managerName: json['manager_name'] as String? ?? '',
         logoUrl: json['logo_url'] as String? ?? '',
         wechatId: json['wechat_id'] as String? ?? '',
+        customFields:
+            (json['custom_fields'] as Map?)?.cast<String, dynamic>() ??
+                const {},
       );
 }