fix(budget): 版本管理UI字段/状态机对齐 active→draft映射+plan_count/last_updated别名

- list_budget_versions 输出 approval_status(active映射draft)+plan_count+last_updated
- 保留 status/kpi_count/updated_at 原字段兼容（下拉'当前'标记/测试契约）
- 前端提交审批按钮兜底 active（双端保险）
- 修复: 版本行仅复选框无按钮/状态恒草稿/条目数空白/最后更新空白

frontend/src/views/BudgetManagement.vue

@@ -166,7 +166,7 @@
           <el-table-column prop="last_updated" label="最后更新" min-width="150" />
           <el-table-column label="操作" width="200" fixed="right">
             <template #default="{ row }">
-              <el-button v-if="row.approval_status === 'draft'" size="small" @click="submitVersion(row)">提交审批</el-button>
+              <el-button v-if="row.approval_status === 'draft' || row.approval_status === 'active'" size="small" @click="submitVersion(row)">提交审批</el-button>
               <template v-if="row.approval_status === 'submitted'"><el-button size="small" type="success" @click="approveVersion(row, 'approved')">批准</el-button><el-button size="small" type="danger" @click="approveVersion(row, 'rejected')">驳回</el-button></template>
               <el-button v-if="row.approval_status === 'rejected'" size="small" @click="resubmitVersion(row)">重新提交</el-button>
               <el-checkbox v-model="row._selected" @change="onVersionSelect(row)" :disabled="selectedVersions.length >= 2 && !row._selected" style="margin-left:8px;" />