feat: add system params persistence and delivery gate enforcement

V25 migration creates platform_system_param table. SystemParamController replaces localStorage MVP with backend persistence. LicenseSnService.create now checks deliveryGateEnabled flag and blocks SN creation when gate is on but no deliveries completed.

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

web/delivery-platform-ui/src/views/SystemParamsView.vue

@@ -1,31 +1,25 @@
 <script setup>
 import { ref, onMounted } from 'vue'
 import { ElMessage } from 'element-plus'
+import axios from 'axios'
 
-const params = ref({
-  orphanSnStrictValidation: true,
-  deliveryGateEnabled: true,
-  sessionTimeoutMinutes: 60,
-  passwordMinLength: 6,
-})
-
+const params = ref({})
 const loading = ref(false)
 
 async function loadParams() {
   try {
-    const stored = localStorage.getItem('systemParams')
-    if (stored) {
-      params.value = { ...params.value, ...JSON.parse(stored) }
-    }
+    const { data } = await axios.get('/api/v1/system-params')
+    params.value = { ...data }
   } catch {
+    ElMessage.error('加载系统参数失败')
   }
 }
 
 async function saveParams() {
   loading.value = true
   try {
-    localStorage.setItem('systemParams', JSON.stringify(params.value))
-    ElMessage.success('参数已保存（MVP: 存储于浏览器本地）')
+    await axios.put('/api/v1/system-params', params.value)
+    ElMessage.success('参数已保存')
   } catch (e) {
     ElMessage.error('保存失败')
   } finally {
@@ -42,10 +36,10 @@ onMounted(loadParams)
     <el-card shadow="never" style="margin-top:16px;max-width:560px">
       <el-form label-width="200px" label-position="left">
         <el-form-item label="孤儿 SN 严格校验">
-          <el-switch v-model="params.orphanSnStrictValidation" />
+          <el-switch v-model="params.orphanSnStrictValidation" active-value="true" inactive-value="false" />
         </el-form-item>
         <el-form-item label="交付闸门启用">
-          <el-switch v-model="params.deliveryGateEnabled" />
+          <el-switch v-model="params.deliveryGateEnabled" active-value="true" inactive-value="false" />
         </el-form-item>
         <el-form-item label="会话超时（分钟）">
           <el-input-number v-model="params.sessionTimeoutMinutes" :min="5" :max="1440" />