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/GroupList.vue

@@ -5,7 +5,7 @@ import { errorMessage } from "../api/errors";
 import BaseButton from "./BaseButton.vue";
 import BaseInput from "./BaseInput.vue";
 import Icon from "./Icon.vue";
-import { useRowAction } from "../composables/useAction";
+import { useRowAction, useLoad } from "../composables/useAction";
 
 // Admin: groups of people a note can be shared with in one go (#5177). A group is
 // the instance's; anyone can share with it, and a note shared with it reaches whoever
@@ -23,11 +23,16 @@ interface Group {
   members: Person[];
 }
 
-
 const groups = ref<Group[]>([]);
 const accounts = ref<Person[]>([]);
-const loading = ref(true);
-const error = ref("");
+const { loading, error, load } = useLoad(async () => {
+  const [g, a] = await Promise.all([
+    api.get<{ groups: Group[] }>("/api/groups"),
+    api.get<{ accounts: Person[] }>("/api/accounts"),
+  ]);
+  groups.value = g.groups;
+  accounts.value = a.accounts;
+}, "Couldn't load groups.");
 const name = ref("");
 const creating = ref(false);
 const { busy, act } = useRowAction();
@@ -43,22 +48,6 @@ function outside(group: Group): Person[] {
 
 const empty = computed(() => !loading.value && !groups.value.length);
 
-async function load() {
-  error.value = "";
-  try {
-    const [g, a] = await Promise.all([
-      api.get<{ groups: Group[] }>("/api/groups"),
-      api.get<{ accounts: Person[] }>("/api/accounts"),
-    ]);
-    groups.value = g.groups;
-    accounts.value = a.accounts;
-  } catch (e) {
-    error.value = errorMessage(e, "Couldn't load groups.");
-  } finally {
-    loading.value = false;
-  }
-}
-
 function replace(updated: Group) {
   groups.value = groups.value.map((g) => (g.id === updated.id ? updated : g)).sort(byName);
 }