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/ActivityList.vue

@@ -3,6 +3,7 @@ import { onMounted, ref } from "vue";
 import { api } from "../api/client";
 import { errorMessage } from "../api/errors";
 import { formatShortDateTime } from "../notes/datetime";
+import { useLoad } from "../composables/useAction";
 
 // Admin: what has happened to accounts on this instance, newest first (#2939 §5).
 // Kept for `audit_retention_days` (Settings → Security).
@@ -45,28 +46,18 @@ const REFUSALS = new Set([
 
 const events = ref<AuditEvent[]>([]);
 const more = ref(false);
-const loading = ref(true);
+const { loading, error, load } = useLoad(async () => {
+  const res = await page();
+  events.value = res.events;
+  more.value = res.more;
+}, "Couldn't load activity.");
 const loadingMore = ref(false);
-const error = ref("");
 
 async function page(before?: string) {
   const query = before ? `?before=${encodeURIComponent(before)}` : "";
   return api.get<{ events: AuditEvent[]; more: boolean }>(`/api/accounts/activity${query}`);
 }
 
-async function load() {
-  error.value = "";
-  try {
-    const res = await page();
-    events.value = res.events;
-    more.value = res.more;
-  } catch (e) {
-    error.value = errorMessage(e, "Couldn't load activity.");
-  } finally {
-    loading.value = false;
-  }
-}
-
 async function loadMore() {
   const last = events.value[events.value.length - 1];
   if (!last) return;