refactor: 彻底移除 apiSecret 认证方式，仅保留 Bearer + PSK

删除:
- HmacUtil: deriveApiKey/deriveApiSecret/verifyMediabotPsk
- HmacAuthInterceptor: apiSecret 验签/自动创建账户/readBody
- AccountService: generateApiCredentials/registerByInterceptor
- AccountDTO: apiKey 字段
- AuthController: register 返回 apiSecret
- AdminController: generateApiKey 端点
- Users.vue: API Key 列/生成密钥弹窗
- api/index.js: genApiKey

认证方式简化为两种:
  Bearer Token → Web 管理后台
  PSK 签名    → 外部集成客户端

web/src/api/index.js

@@ -45,7 +45,7 @@ export default {
   users: {
     list: () => api.get('/admin/accounts'),
     setTrustLevel: (id, level) => api.post(`/admin/accounts/${id}/trust-level`, null, { params: { level } }),
-    genApiKey: (id) => api.post(`/admin/accounts/${id}/api-key`)
+
   },
   health: () => api.get('/health', { baseURL: '' })
 }

web/src/views/Users.vue

@@ -6,12 +6,6 @@
         <el-table-column prop="id" label="ID" width="60" />
         <el-table-column prop="email" label="邮箱" min-width="180" />
         <el-table-column prop="displayName" label="昵称" width="120" />
-        <el-table-column label="API Key" min-width="180">
-          <template #default="scope">
-            <span v-if="scope.row.apiKey" style="font-family:monospace;font-size:12px">{{ scope.row.apiKey }}</span>
-            <el-tag v-else size="small" type="info">未生成</el-tag>
-          </template>
-        </el-table-column>
         <el-table-column prop="trustLevel" label="信任等级" width="90">
           <template #default="scope">
             <el-tag :type="trustLevelType(scope.row.trustLevel)">
@@ -27,45 +21,19 @@
           </template>
         </el-table-column>
         <el-table-column prop="createdAt" label="注册时间" width="160" />
-        <el-table-column label="操作" width="200" fixed="right">
+        <el-table-column label="操作" width="120" fixed="right">
           <template #default="scope">
-            <el-button size="small" @click="handleGenKey(scope.row)">生成密钥</el-button>
             <el-button
               v-if="scope.row.trustLevel !== 'ADMIN'"
               size="small"
               @click="handleSetLevel(scope.row)"
             >设置等级</el-button>
+            <span v-else style="color:#999;font-size:12px">管理员</span>
           </template>
         </el-table-column>
       </el-table>
     </el-card>
 
-    <!-- API Key 弹窗 -->
-    <el-dialog v-model="keyDialogVisible" title="API Key" width="500px" :close-on-click-modal="false">
-      <el-alert type="warning" :closable="false" style="margin-bottom:16px">
-        Secret 仅在生成时显示一次，请立即复制保存！
-      </el-alert>
-      <el-form label-width="80px">
-        <el-form-item label="API Key">
-          <el-input v-model="keyResult.apiKey" readonly>
-            <template #append>
-              <el-button @click="copyText(keyResult.apiKey)">复制</el-button>
-            </template>
-          </el-input>
-        </el-form-item>
-        <el-form-item label="API Secret">
-          <el-input v-model="keyResult.apiSecret" readonly type="textarea" :rows="2">
-            <template #append>
-              <el-button @click="copyText(keyResult.apiSecret)">复制</el-button>
-            </template>
-          </el-input>
-        </el-form-item>
-      </el-form>
-      <template #footer>
-        <el-button @click="keyDialogVisible = false">关闭</el-button>
-      </template>
-    </el-dialog>
-
     <!-- 等级设置弹窗 -->
     <el-dialog v-model="dialogVisible" title="设置信任等级" width="400px">
       <el-form :model="levelForm">
@@ -95,9 +63,6 @@ const loading = ref(false)
 const dialogVisible = ref(false)
 const saving = ref(false)
 const levelForm = reactive({ id: null, email: '', level: '' })
-const keyDialogVisible = ref(false)
-const keyResult = reactive({ apiKey: '', apiSecret: '' })
-
 const trustLevelType = (level) => {
   const map = { MEMBER: '', TRUSTED: 'warning', ADMIN: 'danger' }
   return map[level] || ''
@@ -120,22 +85,6 @@ const fetchUsers = async () => {
   }
 }
 
-const handleGenKey = async (row) => {
-  try {
-    const res = await api.users.genApiKey(row.id)
-    keyResult.apiKey = res.data.apiKey
-    keyResult.apiSecret = res.data.apiSecret
-    keyDialogVisible.value = true
-    fetchUsers()
-  } catch (e) {
-    ElMessage.error(e.response?.data?.message || '生成失败')
-  }
-}
-
-const copyText = (text) => {
-  navigator.clipboard.writeText(text).then(() => ElMessage.success('已复制'))
-}
-
 const handleSetLevel = (row) => {
   levelForm.id = row.id
   levelForm.email = row.email