React 19: useRef<T>() -> useRef<T>(null) across 15 sites

React 19 dropped the no-arg useRef overload — the type-only useRef<T>()
form (no initial value) is gone, every call must pass an initial value.
The codebase had 15 occurrences of useRef<HTMLDivElement>() (DOM ref
pattern) all flagged by tsgo as 'Expected 1 arguments, but got 0'.

Mechanical sweep to useRef<HTMLDivElement>(null) — no behavior change,
React still hands out a ref object with .current set to null at mount.

Net tsgo error count: 57 -> 42.

src/components/room/widgets/object-location/ObjectLocationView.tsx

@@ -14,7 +14,7 @@ export const ObjectLocationView: FC<ObjectLocationViewProps> = props =>
 {
     const { objectId = -1, category = -1, noFollow = false, ...rest } = props;
     const [ pos, setPos ] = useState<{ x: number, y: number }>({ x: -1, y: -1 });
-    const elementRef = useRef<HTMLDivElement>();
+    const elementRef = useRef<HTMLDivElement>(null);
 
     useEffect(() =>
     {