fix(events): clamp page state when totalPages drops below current page (#442)

Bulk-deleting all events on the current page left the list empty until
manual reload. After the React Query refetch returned `events: []` with
a smaller `totalPages`, the page state was stuck on the old (now
out-of-range) page index — the backend correctly serves an empty page
for `page > totalPages`, but the UI had no logic to step back.

Add a useEffect that watches `data.pagination.totalPages` against the
current `page` and resets `page = max(1, totalPages)` whenever the
result count shrinks. Fires after every refetch so it covers bulk
delete, individual delete, archive, and any filter change that
shrinks the result set — same one-line guarantee.

Reported by @Rekoo-PS in #442.

frontend/src/pages/admin/EventsListPage.tsx

@@ -104,6 +104,17 @@ export const EventsListPage: React.FC = () => {
     setPage(1);
   }, [statusFilter, debouncedSearchTerm]);
 
+  // Clamp the active page when the result count shrinks (#442 — bulk
+  // delete of an entire page would leave the user on a now-empty
+  // page=N where N > totalPages, with no auto-correction). Triggers
+  // after each successful refetch when totalPages drops below the
+  // current page (bulk delete, individual delete, archive, anything).
+  useEffect(() => {
+    if (data?.pagination && page > data.pagination.totalPages) {
+      setPage(Math.max(1, data.pagination.totalPages));
+    }
+  }, [data?.pagination, page]);
+
   // Close dropdown when clicking outside
   useEffect(() => {
     const handleClickOutside = (event: MouseEvent) => {