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

frontend/src/features/admin/api/adminDistribution.ts

@@ -119,6 +119,17 @@ export async function fetchDistributionSites() {
   return data.data.items ?? []
 }
 
+export interface DistributionSiteDefaults {
+  default_settlement_hold_days: number
+}
+
+export async function fetchDistributionSiteDefaults() {
+  const { data } = await apiClient.get<ApiResponse<DistributionSiteDefaults>>(
+    '/admin/distribution/site-defaults'
+  )
+  return data.data
+}
+
 export async function onboardDistributionSite(payload: OnboardDistributionSitePayload) {
   const { data } = await apiClient.post<ApiResponse<OnboardDistributionSiteResult>>(
     '/admin/distribution/sites/onboard',

frontend/src/features/admin/views/AdminDistributionSitesView.vue

@@ -4,6 +4,7 @@ import { ElMessage, type FormInstance, type FormRules } from 'element-plus'
 import { Plus, Shop, Link, DocumentCopy, Refresh, Clock } from '@element-plus/icons-vue'
 import {
   fetchDistributionSites,
+  fetchDistributionSiteDefaults,
   onboardDistributionSite,
   syncDistributionSiteAccounts,
   updateDistributionSite,
@@ -16,6 +17,7 @@ import { readError } from '@/shared/utils/error'
 
 const loading = ref(false)
 const sites = ref<DistributionSite[]>([])
+const defaultSettlementHoldDays = ref(7)
 
 const onboardDialogVisible = ref(false)
 const submitting = ref(false)
@@ -29,13 +31,13 @@ const settlementSubmitting = ref(false)
 const settlementForm = reactive({
   site_id: 0,
   site_name: '',
-  settlement_hold_days: 7,
+  settlement_hold_days: defaultSettlementHoldDays.value,
 })
 
 function handleOpenSettlement(row: DistributionSite) {
   settlementForm.site_id = row.id
   settlementForm.site_name = row.site_name
-  settlementForm.settlement_hold_days = row.settlement_hold_days ?? 7
+  settlementForm.settlement_hold_days = row.settlement_hold_days ?? defaultSettlementHoldDays.value
   settlementDialogVisible.value = true
 }
 
@@ -63,7 +65,7 @@ const onboardForm = reactive({
   admin_password: '',
   admin_nickname: '',
   member_type: 'operator',
-  settlement_hold_days: 7,
+  settlement_hold_days: defaultSettlementHoldDays.value,
   display_account_enabled: true,
   tax_enabled: false,
   tax_rate_bps: 100,
@@ -102,7 +104,7 @@ function handleOpenOnboard() {
   onboardForm.admin_password = ''
   onboardForm.admin_nickname = ''
   onboardForm.member_type = 'operator'
-  onboardForm.settlement_hold_days = 7
+  onboardForm.settlement_hold_days = defaultSettlementHoldDays.value
   onboardForm.display_account_enabled = true
   onboardForm.tax_enabled = false
   onboardForm.tax_rate_bps = 100
@@ -171,6 +173,16 @@ async function handleSyncAccounts(row: DistributionSite) {
 
 onMounted(() => {
   loadSites()
+  fetchDistributionSiteDefaults()
+    .then(res => {
+      const days = res?.default_settlement_hold_days
+      if (typeof days === 'number' && days >= 0 && days <= 365) {
+        defaultSettlementHoldDays.value = days
+      }
+    })
+    .catch(() => {
+      // 拉取失败时保持内置默认值 7，不弹错误提示
+    })
 })
 </script>