refactor(admin): unify webui fetch/copy/format helpers; fix audit tab load and delete-group count

- apiFetch + shared needLogin (any 401 shows the login card) replaces six
  duplicated fetch/401/error-handling blocks in the admin composables
- useCopy composable: clipboard + execCommand fallback with timed reset,
  used by MembersPanel and WebhookPanel
- utils/format.ts (fmtTime/splitList/parseMatch) removes inline duplicates
  across SendLogs, AuditLog, RouteEditor and GroupEditor
- fix: load the audit log when the audit tab becomes active (client-side
  navigation never remounted the page, leaving the list empty on first visit)
- fix: fetch the real route count for a group before confirming deletion
  instead of reusing the currently open group's route list

app/components/AuditLog.vue

@@ -70,10 +70,6 @@ const emit = defineEmits<{
   (e: "update:selectedGroupId", value: string): void;
 }>();
 
-function fmtTime(ts: number): string {
-  return new Date(ts).toLocaleString();
-}
-
 function refresh(): void {
   emit("refresh");
 }