feat(distribution): 默认结算冷却天数改为系统配置驱动

新建站点的默认冷却期原先硬编码 7 天（OnboardSite 字面量、DB 列默认、两套前端表单），
改一处要同时动三处。现统一到系统配置键 distribution.default_settlement_hold_days：

- systemconfig 注册该键（默认 7，0=立即释放，0-365 校验），纳入 admin 可见配置
- distribution 建站两条路径（CreateSite 未传值、OnboardSite 缺省）读取该配置，缺失或非法回落 7
- 新增 GET /admin/distribution/site-defaults 暴露当前有效默认值
- Vue / React 站点表单改为运行时拉取，拉取失败保持 7
- DB 列默认值保留作为兜底，站点级 settlement_hold_days 仍可单独覆盖

backend/internal/modules/systemconfig/distribution.go

@@ -0,0 +1,43 @@
+package systemconfig
+
+import (
+	"strconv"
+	"strings"
+)
+
+// DistributionSettlementHoldDaysKey 是「新建分销站点默认结算冷却天数」的系统配置键。
+const DistributionSettlementHoldDaysKey = "distribution.default_settlement_hold_days"
+
+// DefaultDistributionSettlementHoldDays 是新建分销站点默认结算冷却天数的兜底值。
+const DefaultDistributionSettlementHoldDays = 7
+
+func defaultDistributionSettlementHoldDaysValue() string {
+	return strconv.Itoa(DefaultDistributionSettlementHoldDays)
+}
+
+// ParseDistributionSettlementHoldDays 解析结算冷却天数配置，为空、非法或越界时回落到默认 7 天。
+func ParseDistributionSettlementHoldDays(raw string) int {
+	days, err := strconv.Atoi(strings.TrimSpace(raw))
+	if err != nil || days < 0 || days > 365 {
+		return DefaultDistributionSettlementHoldDays
+	}
+	return days
+}
+
+// validateConfigValue 按配置键分发校验逻辑，未注册校验的键直接放行。
+func validateConfigValue(key, value string) error {
+	switch key {
+	case DistributionSettlementHoldDaysKey:
+		return validateDistributionSettlementHoldDays(value)
+	default:
+		return nil
+	}
+}
+
+func validateDistributionSettlementHoldDays(value string) error {
+	days, err := strconv.Atoi(strings.TrimSpace(value))
+	if err != nil || days < 0 || days > 365 {
+		return ErrInvalidConfig
+	}
+	return nil
+}

backend/internal/modules/systemconfig/distribution_test.go

@@ -0,0 +1,66 @@
+package systemconfig
+
+import "testing"
+
+func TestParseDistributionSettlementHoldDays(t *testing.T) {
+	cases := []struct {
+		name string
+		raw  string
+		want int
+	}{
+		{name: "零天立即释放", raw: "0", want: 0},
+		{name: "默认七天", raw: "7", want: 7},
+		{name: "上限三百六十五天", raw: "365", want: 365},
+		{name: "负数回落", raw: "-1", want: DefaultDistributionSettlementHoldDays},
+		{name: "超过上限回落", raw: "366", want: DefaultDistributionSettlementHoldDays},
+		{name: "空值回落", raw: "  ", want: DefaultDistributionSettlementHoldDays},
+		{name: "非数字回落", raw: "abc", want: DefaultDistributionSettlementHoldDays},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := ParseDistributionSettlementHoldDays(tc.raw); got != tc.want {
+				t.Fatalf("ParseDistributionSettlementHoldDays(%q) = %d, want %d", tc.raw, got, tc.want)
+			}
+		})
+	}
+}
+
+func TestDistributionSettlementHoldDaysConfigRegistered(t *testing.T) {
+	value := ""
+	for _, item := range defaultConfigs {
+		if item.Key == DistributionSettlementHoldDaysKey {
+			value = item.Value
+			break
+		}
+	}
+	if value != defaultDistributionSettlementHoldDaysValue() {
+		t.Fatalf("defaultConfigs 中 %s 的默认值 = %q, want %q", DistributionSettlementHoldDaysKey, value, defaultDistributionSettlementHoldDaysValue())
+	}
+	visible := false
+	for _, key := range adminVisibleConfigKeys {
+		if key == DistributionSettlementHoldDaysKey {
+			visible = true
+			break
+		}
+	}
+	if !visible {
+		t.Fatalf("adminVisibleConfigKeys 缺少 %s", DistributionSettlementHoldDaysKey)
+	}
+}
+
+func TestValidateConfigValueDistributionSettlementHoldDays(t *testing.T) {
+	for _, value := range []string{"0", "7", "365"} {
+		if err := validateConfigValue(DistributionSettlementHoldDaysKey, value); err != nil {
+			t.Fatalf("validateConfigValue(%q) = %v, want nil", value, err)
+		}
+	}
+	for _, value := range []string{"-1", "366", "", "abc"} {
+		if err := validateConfigValue(DistributionSettlementHoldDaysKey, value); err != ErrInvalidConfig {
+			t.Fatalf("validateConfigValue(%q) = %v, want ErrInvalidConfig", value, err)
+		}
+	}
+	// 未注册校验的键直接放行。
+	if err := validateConfigValue("handoff.owner_submit_timeout_minutes", "abc"); err != nil {
+		t.Fatalf("无关配置键应放行, got %v", err)
+	}
+}

backend/internal/modules/systemconfig/repository.go

@@ -54,6 +54,7 @@ var defaultConfigs = []defaultConfig{
 	{Key: cooperationFeedbackConfigKey, Value: defaultCooperationFeedbackConfigValue(), Description: "首页 合作与反馈入口配置 JSON（标题/副标题/展示图片）"},
 	{Key: publishOptionsConfigKey, Value: defaultPublishOptionsConfigValue(), Description: "发布页选项配置 JSON"},
 	{Key: salePriceConfigKey, Value: defaultSalePriceConfigValue(), Description: "内部出售定价规则 JSON"},
+	{Key: DistributionSettlementHoldDaysKey, Value: defaultDistributionSettlementHoldDaysValue(), Description: "新建分销站点默认结算冷却天数（0=立即释放，最大 365）"},
 	{Key: "backup.schedule_enabled", Value: "true", Description: "在线备份定时任务是否启用"},
 	{Key: "backup.full_hour", Value: "4", Description: "每日全量备份小时（Asia/Shanghai）"},
 	{Key: "backup.full_minute", Value: "30", Description: "每日全量备份分钟（Asia/Shanghai）"},
@@ -65,6 +66,7 @@ var adminVisibleConfigKeys = []string{
 	"chat.default_support_admin_id",
 	"chat.listing_group_welcome",
 	"chat.renter_retention_days_after_order_end",
+	"distribution.default_settlement_hold_days",
 	"handoff.owner_return_confirm_timeout_minutes",
 	"handoff.owner_submit_timeout_minutes",
 	"handoff.renter_confirm_timeout_minutes",
@@ -140,6 +142,9 @@ func (r *Repository) FindValue(ctx context.Context, key string) (string, error)
 }
 
 func (r *Repository) Update(ctx context.Context, actorID uint64, key string, req UpdateRequest, meta AuditMeta) (*ConfigDTO, error) {
+	if err := validateConfigValue(key, req.Value); err != nil {
+		return nil, err
+	}
 	var row model.SystemConfig
 	err := r.db.WithContext(ctx).Transaction(func(tx *gorm.DB) error {
 		if err := tx.Clauses(clause.Locking{Strength: "UPDATE"}).Where("`key` = ?", key).First(&row).Error; err != nil {