fix(data-lit): propagate {} | null constraint to useDragTransaction type param

withFilter gained U extends {} | null in #127; useDragTransaction's unconstrained
T no longer satisfies it. Constraining T here aligns the type throughout the
call chain and reflects the genuine semantic — a transaction arg of undefined
makes no sense.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: krisnye

packages/data-lit/src/hooks/use-drag-transaction.ts

@@ -5,12 +5,12 @@ import { useEffect } from "./use-effect.js";
 import type { AsyncArgsProvider } from '@adobe/data/ecs';
 import { Observe } from '@adobe/data/observe';
 
-export type DragTransactionProps<T> = DragObserveProps & {
+export type DragTransactionProps<T extends {} | null> = DragObserveProps & {
     transaction: (asyncArgs: AsyncArgsProvider<T>) => void;
     update: (drag: DragMove | DragEnd) => T | void;
 };
 
-export function useDragTransaction<T>(props: DragTransactionProps<T>, dependencies: unknown[]) {
+export function useDragTransaction<T extends {} | null>(props: DragTransactionProps<T>, dependencies: unknown[]) {
     const { transaction, update } = props;
     const dragObserve = useDragObserve(props, dependencies);
     const startDragTransaction = () => {