ui: clarify global vs project-level policies in frontend

- Rename "权限策略" to "全局权限策略" in dropdown menu
- Add info banner explaining global vs project-level in both dialogs
- Disable already-attached policies in global dropdown (grey out)
- Show policy type as tag (系统/自定义) in global policies table

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/views/iam/IAMUserList.vue

@@ -82,7 +82,7 @@
                   <el-dropdown-item @click="toggleVolcLogin(row)">
                     {{ row.volc_login_allowed ? '🔓 关闭火山登录' : '🔒 开启火山登录' }}
                   </el-dropdown-item>
-                  <el-dropdown-item @click="openPolicies(row)">权限策略</el-dropdown-item>
+                  <el-dropdown-item @click="openPolicies(row)">全局权限策略</el-dropdown-item>
                   <el-dropdown-item @click="openQuotaHistory(row)">划拨记录</el-dropdown-item>
                   <el-dropdown-item @click="openSetLogin(row)">登录密码</el-dropdown-item>
                   <el-dropdown-item v-if="row.status === 'active'" divided
@@ -221,11 +221,13 @@
 
     <!-- Project Policies Dialog -->
     <el-dialog v-model="projectPolicyVisible"
-               :title="`${projectPolicyProject?.project_name} 项目授权`"
+               :title="`${projectPolicyProject?.project_name} 项目级授权`"
                width="90%" style="max-width: 550px;">
-      <p style="margin-bottom:12px; color:#606266; font-size:13px;">
-        子账号 <strong>{{ projectsUser?.username }}</strong> 在此项目下的权限：
-      </p>
+      <el-alert type="info" :closable="false" style="margin-bottom:12px;">
+        <template #title>
+          以下权限仅在 <strong>{{ projectPolicyProject?.project_name }}</strong> 项目范围内生效，不影响其他项目。
+        </template>
+      </el-alert>
       <el-checkbox-group v-model="projectPolicySelected">
         <div style="display:flex; flex-direction:column; gap:8px;">
           <el-checkbox label="ArkFullAccess">方舟/Seedance 完整权限</el-checkbox>
@@ -282,25 +284,33 @@
       </el-table>
     </el-dialog>
 
-    <!-- Policies Dialog -->
-    <el-dialog v-model="policiesVisible" :title="`${policiesUser?.username} 权限策略`" width="90%" style="max-width: 850px;">
+    <!-- Policies Dialog (Global) -->
+    <el-dialog v-model="policiesVisible" :title="`${policiesUser?.username} 全局权限策略`" width="90%" style="max-width: 850px;">
+      <el-alert type="info" :closable="false" style="margin-bottom:12px;">
+        <template #title>
+          <strong>全局策略</strong>对所有项目生效。如需限定到某个项目，请在「项目管理 → 授权」中设置项目级策略。
+        </template>
+      </el-alert>
       <div style="margin-bottom:12px; display:flex; gap:8px;">
         <el-select v-model="policyToAttach" placeholder="选择要附加的策略" filterable style="flex:1;">
           <el-option-group label="常用策略">
-            <el-option value="ArkFullAccess" label="ArkFullAccess（方舟/Seedance 完整权限）" />
-            <el-option value="ArkExperienceAccess" label="ArkExperienceAccess（方舟体验权限）" />
-            <el-option value="ArkReadOnlyAccess" label="ArkReadOnlyAccess（方舟只读）" />
-            <el-option value="TOSFullAccess" label="TOSFullAccess（对象存储完整权限）" />
-            <el-option value="TOSReadOnlyAccess" label="TOSReadOnlyAccess（对象存储只读）" />
-            <el-option value="AccessKeySelfManageAccess" label="AccessKeySelfManageAccess（自管理密钥）" />
+            <el-option v-for="opt in globalPolicyOptions" :key="opt.value"
+              :value="opt.value" :label="opt.label"
+              :disabled="policies.some(p => p.PolicyName === opt.value)" />
           </el-option-group>
         </el-select>
         <el-button type="primary" @click="handleAttachPolicy" :disabled="!policyToAttach">附加</el-button>
       </div>
       <el-table :data="policies" stripe v-loading="policiesLoading" empty-text="暂无策略">
-        <el-table-column prop="PolicyName" label="策略名" />
-        <el-table-column prop="PolicyType" label="类型" width="80" />
-        <el-table-column prop="Description" label="说明" />
+        <el-table-column prop="PolicyName" label="策略名" min-width="200" />
+        <el-table-column prop="PolicyType" label="类型" width="80">
+          <template #default="{ row }">
+            <el-tag :type="row.PolicyType === 'Custom' ? 'warning' : 'info'" size="small">
+              {{ row.PolicyType === 'Custom' ? '自定义' : '系统' }}
+            </el-tag>
+          </template>
+        </el-table-column>
+        <el-table-column prop="Description" label="说明" min-width="200" />
         <el-table-column label="操作" width="80">
           <template #default="{ row }">
             <el-button size="small" type="danger" text @click="handleDetachPolicy(row)">移除</el-button>
@@ -478,6 +488,16 @@ async function handleEnable(row) {
   }
 }
 
+// Global policy options
+const globalPolicyOptions = [
+  { value: 'ArkFullAccess', label: 'ArkFullAccess（方舟/Seedance 完整权限）' },
+  { value: 'ArkExperienceAccess', label: 'ArkExperienceAccess（方舟体验权限）' },
+  { value: 'ArkReadOnlyAccess', label: 'ArkReadOnlyAccess（方舟只读）' },
+  { value: 'TOSFullAccess', label: 'TOSFullAccess（对象存储完整权限）' },
+  { value: 'TOSReadOnlyAccess', label: 'TOSReadOnlyAccess（对象存储只读）' },
+  { value: 'AccessKeySelfManageAccess', label: 'AccessKeySelfManageAccess（自管理密钥）' },
+]
+
 // Toggle Volcengine console login
 async function toggleVolcLogin(row) {
   const action = row.volc_login_allowed ? '关闭' : '开启'