feat(mail): 增强邮件限流与配额配置

- 新增 IMAP/POP3 事件表与清理任务，并接入 Dovecot auth policy。
- 暴露默认权限限额接口，前端权限组页面改为动态读取。
- 为 Dovecot 配置用户配额、连接数限制和 auth policy。

apps/web/src/lib/api.ts

@@ -66,6 +66,7 @@ export const api = {
   permissionGroups: () => request<ListResponse<PermissionGroup> & { catalog: PermissionInfo[] }>("/api/admin/permission-groups"),
   createPermissionGroup: (payload: { name: string; description: string; permissions: PermissionKey[]; limits: PermissionLimits }) => request<PermissionGroup>("/api/admin/permission-groups", { method: "POST", body: JSON.stringify(payload) }),
   updatePermissionGroup: (id: string, payload: { name: string; description: string; permissions: PermissionKey[]; limits: PermissionLimits }) => request<PermissionGroup>(`/api/admin/permission-groups/${id}`, { method: "POST", body: JSON.stringify(payload) }),
+  defaultPermissionLimits: () => request<PermissionLimits>("/api/admin/permission-limits/defaults"),
   deletePermissionGroup: (id: string) => request<{ ok: boolean }>(`/api/admin/permission-groups/${id}`, { method: "DELETE" }),
   createUser: (payload: { email: string; displayName: string; role: "admin" | "user"; password: string; disabled: boolean; permissionGroupIds?: string[] }) => request<AdminUser>("/api/admin/users", { method: "POST", body: JSON.stringify(payload) }),
   updateUser: (id: string, payload: { displayName: string; role: "admin" | "user"; disabled: boolean; permissionGroupIds?: string[] }) => request<AdminUser>(`/api/admin/users/${id}`, { method: "POST", body: JSON.stringify(payload) }),

apps/web/src/pages/admin.tsx

@@ -368,6 +368,8 @@ function PermissionGroupDialog({ group, catalog, open, onOpenChange }: { group?:
   const [internalOpen, setInternalOpen] = React.useState(false)
   const dialogOpen = open ?? internalOpen
   const setDialogOpen = onOpenChange ?? setInternalOpen
+  const defaultLimitsQuery = useQuery({ queryKey: ["admin", "permission-limits", "defaults"], queryFn: api.defaultPermissionLimits, enabled: dialogOpen })
+  const defaultLimits = defaultLimitsQuery.data || defaultPermissionLimits
   const [permissions, setPermissions] = React.useState<PermissionKey[]>(group?.permissions || [])
   const [limits, setLimits] = React.useState<PermissionLimits>(group?.limits || defaultPermissionLimits)
   React.useEffect(() => {
@@ -514,7 +516,8 @@ function PermissionBadges({ permissions, catalog }: { permissions: PermissionKey
 }
 
 function PermissionLimitBadges({ limits }: { limits?: PermissionLimits }) {
-  const value = limits || defaultPermissionLimits
+  const defaultLimitsQuery = useQuery({ queryKey: ["admin", "permission-limits", "defaults"], queryFn: api.defaultPermissionLimits })
+  const value = limits || defaultLimitsQuery.data || defaultPermissionLimits
   return (
     <div className="mt-3 flex flex-wrap gap-1.5">
       <Badge variant="secondary" className="font-normal">附件 {limitText(value.maxAttachmentMb, "MB")}</Badge>