DRY pass #2, batch 5, F16: the admin lists load through useLoad (#5372)

Accounts, groups, invites and activity each wrote the same first load:
clear the error, try, put the server's reason or a fallback in error,
and stop loading. useLoad (composables/useAction.ts) is that, and its
load() is also the retry.

Kept: ShareDialog and Settings. Their load sets loading back to true on a
reload, which the lists never did, so moving them would change what a
retry shows.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/components/InviteList.vue

@@ -6,7 +6,7 @@ import { appLink } from "../router/links";
 import BaseButton from "./BaseButton.vue";
 import BaseInput from "./BaseInput.vue";
 import OneTimeLink from "./OneTimeLink.vue";
-import { toastOnFailure } from "../composables/useAction";
+import { toastOnFailure, useLoad } from "../composables/useAction";
 
 // Admin: invite one person to register while registration stays closed (#5172).
 // The server keeps only a hash of each invite's token, so the link is shown once,
@@ -30,25 +30,15 @@ const LIFETIMES = [
 ];
 
 const invites = ref<Invite[]>([]);
-const loading = ref(true);
-const error = ref("");
+const { loading, error, load } = useLoad(async () => {
+  invites.value = (await api.get<{ invites: Invite[] }>("/api/invites")).invites;
+}, "Couldn't load invites.");
 const email = ref("");
 const days = ref(7);
 const creating = ref(false);
 // The link for the invite just made. Never retrievable again once dismissed.
 const freshLink = ref("");
 
-async function load() {
-  error.value = "";
-  try {
-    invites.value = (await api.get<{ invites: Invite[] }>("/api/invites")).invites;
-  } catch (e) {
-    error.value = errorMessage(e, "Couldn't load invites.");
-  } finally {
-    loading.value = false;
-  }
-}
-
 async function create() {
   creating.value = true;
   error.value = "";