Refactor data fetching hooks, add page size lint test

- Simplify useFetchData: remove unused URL building logic
- Add usePolledData initial implementation
- Add router page_size param validation test
- Update API reference docs
- Clean up tasks doc

frontend/src/hooks/usePolledData.ts

@@ -195,7 +195,7 @@ export function usePolledData<TResponse, TData>(
     if (!refetchOnWindowFocus) return;
 
     const onFocus = (): void => {
-      refreshRef.current();
+      refreshRef.current?.();
     };
 
     window.addEventListener("focus", onFocus);