fix(portal): localPart is string | undefined under noUncheckedIndexedAccess

split('@')[0] needs a fallback even though the email regex guarantees the
separator — portal typecheck (CI) rejected the mobileconfig route.

apps/portal/server/api/apple-mailconfig.get.ts

@@ -36,7 +36,8 @@ export default defineEventHandler(async (event) => {
   }
 
   const mailHost = new URL(useRuntimeConfig().public.mailUrl as string).host
-  const localPart = email.split('@')[0]
+  // The regex above guarantees an @, but noUncheckedIndexedAccess doesn't know.
+  const localPart = email.split('@')[0] ?? email
   const accountUuid = randomUUID()
   const profileUuid = randomUUID()
   const e = xmlEscape(email)