feat(ai): 统一 AI 配置入口到 /admin/ai-settings

## 新增
- 创建 /admin/ai-settings 统一配置页（AiProviderSettingsCard + AiUsageDashboard）
- admin 侧边栏新增"AI 配置"菜单项（权限 AI_CONFIGURE，图标 Sparkles）
- 新增 deleteAiProvider 数据访问层（事务删除 + 自动转移默认）
- 新增 deleteAiProviderAction Server Action（Zod 校验 + 权限校验）
- AiProviderSettingsCard 新增删除按钮（AlertDialog 确认 + destructive 变体）
- 新增 i18n 翻译键（delete/deleteConfirm/deleteSuccess 等，zh-CN + en）

## 移除
- 从 /settings 移除 AI 标签页（原 VALID_TABS 含 "ai"，现仅 4 标签页）
- 从考试页面移除 AI 配置弹窗（Dialog + AiProviderSettingsCard 内嵌）
- 从 ai-provider-selector.tsx 移除配置弹窗（managePanel/manageOpen props）
- 移除 settings-view.tsx 中 canConfigureAi 逻辑和未使用 import

## 变更
- 考试页面"管理"按钮改为 Link 跳转到 /admin/ai-settings
- ai-provider-selector.tsx"管理"按钮改为 Link 跳转到 /admin/ai-settings
- exam-form.tsx 移除 providerDialogOpen/providerDialogKey 状态
- 修正架构文档 004 中 Action 命名（getAiProvidersAction → getAiProviderSummaries 等）

## 架构文档同步
- 004 更新 settings 模块章节（V3 标记/修正 Action 名称/新增 deleteAiProvider）
- 005 新增 deleteAiProviderAction 节点 + /admin/ai-settings 路由

src/modules/settings/components/settings-view.tsx

@@ -4,14 +4,13 @@ import Link from "next/link"
 import { useRouter, useSearchParams } from "next/navigation"
 import { Suspense, type ReactNode } from "react"
 import { useTranslations } from "next-intl"
-import { User, Palette, Lock, Bell, Sparkles } from "lucide-react"
+import { User, Palette, Lock, Bell } from "lucide-react"
 import { signOut } from "next-auth/react"
 
 import { ThemePreferencesCard } from "@/modules/settings/components/theme-preferences-card"
 import { ProfileSettingsForm } from "@/modules/settings/components/profile-settings-form"
 import { PasswordChangeForm } from "@/modules/settings/components/password-change-form"
 import { NotificationPreferencesForm } from "@/modules/settings/components/notification-preferences-form"
-import { AiProviderSettingsCard } from "@/modules/settings/components/ai-provider-settings-card"
 import { SecurityCenterCard } from "@/modules/settings/components/security-center-card"
 import { SettingsSectionErrorBoundary } from "@/modules/settings/components/settings-section-error-boundary"
 import { Button } from "@/shared/components/ui/button"
@@ -31,8 +30,6 @@ import {
 } from "@/shared/components/ui/alert-dialog"
 import type { UserProfile } from "@/modules/users/data-access"
 import type { NotificationPreferences } from "@/modules/notifications/types"
-import { usePermission } from "@/shared/hooks/use-permission"
-import { Permissions } from "@/shared/types/permissions"
 
 interface SettingsViewProps {
   /** 页面副标题描述（i18n 键） */
@@ -49,7 +46,7 @@ interface SettingsViewProps {
   currentUserAgent?: string
 }
 
-const VALID_TABS = ["general", "notifications", "appearance", "security", "ai"] as const
+const VALID_TABS = ["general", "notifications", "appearance", "security"] as const
 type TabValue = (typeof VALID_TABS)[number]
 
 function isTabValue(value: string | null): value is TabValue {
@@ -95,15 +92,12 @@ function SettingsViewInner({
   const t = useTranslations("settings")
   const router = useRouter()
   const searchParams = useSearchParams()
-  const { hasPermission } = usePermission()
 
   const tabParam = searchParams.get("tab")
-  const canConfigureAi = hasPermission(Permissions.AI_CONFIGURE)
 
-  // 解析 tab 参数，对无权限的 tab（如非管理员的 ai）回退到 general
+  // 解析 tab 参数
   function resolveTab(value: string | null): TabValue {
     if (!isTabValue(value)) return "general"
-    if (value === "ai" && !canConfigureAi) return "general"
     return value
   }
   const activeTab: TabValue = resolveTab(tabParam)
@@ -151,12 +145,6 @@ function SettingsViewInner({
             <Lock className="h-4 w-4" />
             {t("tabs.security")}
           </TabsTrigger>
-          {canConfigureAi ? (
-            <TabsTrigger value="ai" className="gap-2">
-              <Sparkles className="h-4 w-4" />
-              {t("tabs.ai")}
-            </TabsTrigger>
-          ) : null}
         </TabsList>
 
         <TabsContent value="general" className="mt-6 space-y-6">
@@ -223,16 +211,6 @@ function SettingsViewInner({
             </Suspense>
           </SettingsSectionErrorBoundary>
         </TabsContent>
-
-        {canConfigureAi ? (
-          <TabsContent value="ai" className="mt-6 space-y-6">
-            <SettingsSectionErrorBoundary>
-              <Suspense fallback={<SettingsSectionSkeleton />}>
-                <AiProviderSettingsCard />
-              </Suspense>
-            </SettingsSectionErrorBoundary>
-          </TabsContent>
-        ) : null}
       </Tabs>
     </div>
   )