feat: add admin UI frontend and complete backend APIs

- Add Vue 3 frontend with Element Plus
- Implement login, dashboard, tenant management
- Add app configuration, logs viewer, stats pages
- Add user management for admins
- Update Drone CI to build and deploy frontend
- Frontend ports: 3001 (test), 4001 (prod)

frontend/src/views/users/index.vue

@@ -0,0 +1,169 @@
+<script setup>
+import { ref, reactive, onMounted } from 'vue'
+import { ElMessage, ElMessageBox } from 'element-plus'
+import api from '@/api'
+import { useAuthStore } from '@/stores/auth'
+
+const authStore = useAuthStore()
+
+const loading = ref(false)
+const tableData = ref([])
+
+// 对话框
+const dialogVisible = ref(false)
+const dialogTitle = ref('')
+const formRef = ref(null)
+const form = reactive({
+  username: '',
+  password: '',
+  nickname: '',
+  role: 'viewer'
+})
+
+const rules = {
+  username: [{ required: true, message: '请输入用户名', trigger: 'blur' }],
+  password: [{ required: true, message: '请输入密码', trigger: 'blur' }]
+}
+
+async function fetchList() {
+  loading.value = true
+  try {
+    const res = await api.get('/api/auth/users')
+    tableData.value = res.data || []
+  } catch (e) {
+    console.error(e)
+  } finally {
+    loading.value = false
+  }
+}
+
+function handleCreate() {
+  dialogTitle.value = '新建用户'
+  Object.assign(form, {
+    username: '',
+    password: '',
+    nickname: '',
+    role: 'viewer'
+  })
+  dialogVisible.value = true
+}
+
+async function handleSubmit() {
+  await formRef.value.validate()
+  
+  try {
+    await api.post('/api/auth/users', form)
+    ElMessage.success('创建成功')
+    dialogVisible.value = false
+    fetchList()
+  } catch (e) {
+    // 错误已在拦截器处理
+  }
+}
+
+async function handleDelete(row) {
+  if (row.id === authStore.user?.id) {
+    ElMessage.warning('不能删除当前登录用户')
+    return
+  }
+  
+  await ElMessageBox.confirm(`确定删除用户 "${row.username}" 吗？`, '提示', {
+    type: 'warning'
+  })
+  
+  try {
+    await api.delete(`/api/auth/users/${row.id}`)
+    ElMessage.success('删除成功')
+    fetchList()
+  } catch (e) {
+    // 错误已在拦截器处理
+  }
+}
+
+function getRoleTag(role) {
+  const map = {
+    admin: { type: 'danger', text: '管理员' },
+    operator: { type: 'warning', text: '操作员' },
+    viewer: { type: 'info', text: '只读' }
+  }
+  return map[role] || { type: 'info', text: role }
+}
+
+onMounted(() => {
+  fetchList()
+})
+</script>
+
+<template>
+  <div class="page-container">
+    <div class="page-header">
+      <div class="title">用户管理</div>
+      <el-button type="primary" @click="handleCreate">
+        <el-icon><Plus /></el-icon>
+        新建用户
+      </el-button>
+    </div>
+    
+    <!-- 表格 -->
+    <el-table v-loading="loading" :data="tableData" style="width: 100%">
+      <el-table-column prop="id" label="ID" width="80" />
+      <el-table-column prop="username" label="用户名" width="150" />
+      <el-table-column prop="nickname" label="昵称" width="150" />
+      <el-table-column prop="role" label="角色" width="120">
+        <template #default="{ row }">
+          <el-tag :type="getRoleTag(row.role).type" size="small">
+            {{ getRoleTag(row.role).text }}
+          </el-tag>
+        </template>
+      </el-table-column>
+      <el-table-column prop="status" label="状态" width="100">
+        <template #default="{ row }">
+          <el-tag :type="row.status === 1 ? 'success' : 'danger'" size="small">
+            {{ row.status === 1 ? '启用' : '禁用' }}
+          </el-tag>
+        </template>
+      </el-table-column>
+      <el-table-column prop="last_login_at" label="最后登录" width="180" />
+      <el-table-column prop="created_at" label="创建时间" width="180" />
+      <el-table-column label="操作" width="100" fixed="right">
+        <template #default="{ row }">
+          <el-button 
+            type="danger" 
+            link 
+            size="small" 
+            :disabled="row.id === authStore.user?.id"
+            @click="handleDelete(row)"
+          >
+            删除
+          </el-button>
+        </template>
+      </el-table-column>
+    </el-table>
+    
+    <!-- 新建对话框 -->
+    <el-dialog v-model="dialogVisible" :title="dialogTitle" width="450px">
+      <el-form ref="formRef" :model="form" :rules="rules" label-width="80px">
+        <el-form-item label="用户名" prop="username">
+          <el-input v-model="form.username" placeholder="登录用户名" />
+        </el-form-item>
+        <el-form-item label="密码" prop="password">
+          <el-input v-model="form.password" type="password" show-password placeholder="登录密码" />
+        </el-form-item>
+        <el-form-item label="昵称">
+          <el-input v-model="form.nickname" placeholder="显示名称" />
+        </el-form-item>
+        <el-form-item label="角色">
+          <el-select v-model="form.role" style="width: 100%">
+            <el-option label="管理员" value="admin" />
+            <el-option label="操作员" value="operator" />
+            <el-option label="只读" value="viewer" />
+          </el-select>
+        </el-form-item>
+      </el-form>
+      <template #footer>
+        <el-button @click="dialogVisible = false">取消</el-button>
+        <el-button type="primary" @click="handleSubmit">确定</el-button>
+      </template>
+    </el-dialog>
+  </div>
+</template>