refactor: 移除旧版数据库配置的简易模式实现

移除与 PR #66 冲突的旧版简易模式实现（commit 7d4b7de）。
新版简易模式通过 run_mode 配置文件/环境变量控制，无需数据库设置。

后端变更：
- 移除 SettingKeySimpleMode 常量
- 移除 SystemSettings/PublicSettings 中的 SimpleMode 字段
- 移除 setting_handler 中的简易模式切换逻辑
- 移除 userService 依赖（不再需要自动设置管理员并发数）

前端变更：
- 移除 appStore.simpleMode 状态
- 移除设置页面的"使用模式"设置区块
- 移除 GroupsView 中的简易模式相关逻辑
- 移除相关国际化文案

frontend/src/views/admin/GroupsView.vue

@@ -683,18 +683,10 @@ const editStatusOptions = computed(() => [
   { value: 'inactive', label: t('common.inactive') }
 ])
 
-const subscriptionTypeOptions = computed(() => {
-  // 简单模式下只显示订阅模式（配额模式）
-  if (appStore.simpleMode) {
-    return [
-      { value: 'subscription', label: t('admin.groups.subscription.subscription') }
-    ]
-  }
-  return [
-    { value: 'standard', label: t('admin.groups.subscription.standard') },
-    { value: 'subscription', label: t('admin.groups.subscription.subscription') }
-  ]
-})
+const subscriptionTypeOptions = computed(() => [
+  { value: 'standard', label: t('admin.groups.subscription.standard') },
+  { value: 'subscription', label: t('admin.groups.subscription.subscription') }
+])
 
 const groups = ref<Group[]>([])
 const loading = ref(false)
@@ -804,7 +796,7 @@ const closeCreateModal = () => {
   createForm.platform = 'anthropic'
   createForm.rate_multiplier = 1.0
   createForm.is_exclusive = false
-  createForm.subscription_type = appStore.simpleMode ? 'subscription' : 'standard'
+  createForm.subscription_type = 'standard'
   createForm.daily_limit_usd = null
   createForm.weekly_limit_usd = null
   createForm.monthly_limit_usd = null
@@ -895,9 +887,5 @@ watch(
 
 onMounted(() => {
   loadGroups()
-  // 简单模式下默认使用订阅模式
-  if (appStore.simpleMode) {
-    createForm.subscription_type = 'subscription'
-  }
 })
 </script>

frontend/src/views/admin/SettingsView.vue

@@ -153,58 +153,6 @@
           </div>
         </div>
 
-        <!-- Usage Mode Settings -->
-        <div class="card">
-          <div class="border-b border-gray-100 px-6 py-4 dark:border-dark-700">
-            <h2 class="text-lg font-semibold text-gray-900 dark:text-white">
-              {{ t('admin.settings.usageMode.title') }}
-            </h2>
-            <p class="mt-1 text-sm text-gray-500 dark:text-gray-400">
-              {{ t('admin.settings.usageMode.description') }}
-            </p>
-          </div>
-          <div class="space-y-5 p-6">
-            <!-- Simple Mode Toggle -->
-            <div class="flex items-center justify-between">
-              <div>
-                <label class="font-medium text-gray-900 dark:text-white">
-                  {{ t('admin.settings.usageMode.simpleMode') }}
-                </label>
-                <p class="text-sm text-gray-500 dark:text-gray-400">
-                  {{ t('admin.settings.usageMode.simpleModeHint') }}
-                </p>
-              </div>
-              <Toggle
-                :model-value="form.simple_mode"
-                @update:model-value="onSimpleModeToggle"
-              />
-            </div>
-
-            <!-- Warning when simple mode is enabled -->
-            <div
-              v-if="form.simple_mode"
-              class="rounded-lg border border-amber-200 bg-amber-50 p-4 dark:border-amber-800 dark:bg-amber-900/20"
-            >
-              <div class="flex items-start">
-                <svg
-                  class="mt-0.5 h-5 w-5 flex-shrink-0 text-amber-500"
-                  fill="currentColor"
-                  viewBox="0 0 20 20"
-                >
-                  <path
-                    fill-rule="evenodd"
-                    d="M8.257 3.099c.765-1.36 2.722-1.36 3.486 0l5.58 9.92c.75 1.334-.213 2.98-1.742 2.98H4.42c-1.53 0-2.493-1.646-1.743-2.98l5.58-9.92zM11 13a1 1 0 11-2 0 1 1 0 012 0zm-1-8a1 1 0 00-1 1v3a1 1 0 002 0V6a1 1 0 00-1-1z"
-                    clip-rule="evenodd"
-                  />
-                </svg>
-                <p class="ml-3 text-sm text-amber-700 dark:text-amber-300">
-                  {{ t('admin.settings.usageMode.simpleModeWarning') }}
-                </p>
-              </div>
-            </div>
-          </div>
-        </div>
-
         <!-- Registration Settings -->
         <div class="card">
           <div class="border-b border-gray-100 px-6 py-4 dark:border-dark-700">
@@ -758,19 +706,6 @@
         </div>
       </form>
     </div>
-
-    <!-- Simple Mode Confirmation Dialog -->
-    <ConfirmDialog
-      :show="showSimpleModeConfirm"
-      :title="t('admin.settings.usageMode.confirmTitle')"
-      :message="pendingSimpleModeValue
-        ? t('admin.settings.usageMode.confirmEnableMessage')
-        : t('admin.settings.usageMode.confirmDisableMessage')"
-      :confirm-text="t('common.confirm')"
-      :cancel-text="t('common.cancel')"
-      @confirm="confirmSimpleModeChange"
-      @cancel="cancelSimpleModeChange"
-    />
   </AppLayout>
 </template>
 
@@ -781,7 +716,6 @@ import { adminAPI } from '@/api'
 import type { SystemSettings } from '@/api/admin/settings'
 import AppLayout from '@/components/layout/AppLayout.vue'
 import Toggle from '@/components/common/Toggle.vue'
-import ConfirmDialog from '@/components/common/ConfirmDialog.vue'
 import { useAppStore } from '@/stores'
 
 const { t } = useI18n()
@@ -794,10 +728,6 @@ const sendingTestEmail = ref(false)
 const testEmailAddress = ref('')
 const logoError = ref('')
 
-// Simple mode confirmation dialog
-const showSimpleModeConfirm = ref(false)
-const pendingSimpleModeValue = ref(false)
-
 // Admin API Key 状态
 const adminApiKeyLoading = ref(true)
 const adminApiKeyExists = ref(false)
@@ -826,9 +756,7 @@ const form = reactive<SystemSettings>({
   // Cloudflare Turnstile
   turnstile_enabled: false,
   turnstile_site_key: '',
-  turnstile_secret_key: '',
-  // Usage mode
-  simple_mode: false
+  turnstile_secret_key: ''
 })
 
 function handleLogoUpload(event: Event) {
@@ -899,40 +827,6 @@ async function saveSettings() {
   }
 }
 
-// Simple mode toggle handlers
-function onSimpleModeToggle(value: boolean) {
-  pendingSimpleModeValue.value = value
-  showSimpleModeConfirm.value = true
-}
-
-async function confirmSimpleModeChange() {
-  showSimpleModeConfirm.value = false
-  form.simple_mode = pendingSimpleModeValue.value
-
-  saving.value = true
-  try {
-    await adminAPI.settings.updateSettings(form)
-    await appStore.fetchPublicSettings(true)
-    appStore.showSuccess(t('admin.settings.settingsSaved'))
-    // Reload page to apply menu changes
-    setTimeout(() => {
-      window.location.reload()
-    }, 500)
-  } catch (error: any) {
-    // Revert on error
-    form.simple_mode = !pendingSimpleModeValue.value
-    appStore.showError(
-      t('admin.settings.failedToSave') + ': ' + (error.message || t('common.unknownError'))
-    )
-  } finally {
-    saving.value = false
-  }
-}
-
-function cancelSimpleModeChange() {
-  showSimpleModeConfirm.value = false
-}
-
 async function testSmtpConnection() {
   testingSmtp.value = true
   try {