fix(auth): fail closed configuration compatibility

backend/src/auth/auth.ts

@@ -1,12 +1,11 @@
 import type { FastifyRequest, FastifyReply } from "fastify";
 import { localPrincipal, type PrincipalContext, upstreamPrincipal } from "./principal.js";
-import type { AuthMode } from "./types.js";
 
 declare module "fastify" {
   interface FastifyRequest { principal?: PrincipalContext }
 }
 
-export function authPreHandler(mode: AuthMode) {
+export function authPreHandler(mode: "none" | "mock" | "upstream") {
   return async (req: FastifyRequest, reply: FastifyReply) => {
     if (mode === "none") {
       req.principal = localPrincipal();