fix(react-form): restore optional selector in useStore re-export

Prior to @tanstack/react-store 0.9.1, useStore could be called with just
a store reference and no selector, which returned the full atom snapshot:

  const formState = useStore(form.store)

The 0.9.1 update made the selector argument required in TypeScript types,
causing a build error in existing code using the single-argument form.

Instead of re-exporting useStore directly, add a thin overload wrapper in
packages/react-form/src/useStore.ts that makes the selector optional and
preserves backward-compatible types while delegating to the underlying
@tanstack/react-store implementation.

Fixes #2074

Author: mixelburg

packages/react-form/src/index.ts

@@ -1,6 +1,6 @@
 export * from '@tanstack/form-core'
 
-export { useStore } from '@tanstack/react-store'
+export { useStore } from './useStore'
 
 export * from './createFormHook'
 export * from './types'

packages/react-form/src/useStore.ts

@@ -0,0 +1,44 @@
+import { useStore as _useStore } from '@tanstack/react-store'
+import type { AnyAtom } from '@tanstack/store'
+
+type AtomSnapshot<TAtom> = TAtom extends { get: () => infer TSnapshot }
+  ? TSnapshot
+  : undefined
+
+/**
+ * Subscribe to a store atom and return its current state.
+ *
+ * When called without a `selector` the full atom snapshot is returned.
+ *
+ * @example
+ * // Return the full form state (selector optional for back-compat)
+ * const formState = useStore(form.store)
+ *
+ * @example
+ * // Return a specific slice
+ * const isValid = useStore(form.store, (s) => s.isValid)
+ */
+export function useStore<TAtom extends AnyAtom | undefined>(
+  atom: TAtom,
+): AtomSnapshot<TAtom>
+
+export function useStore<TAtom extends AnyAtom | undefined, T>(
+  atom: TAtom,
+  selector: (snapshot: AtomSnapshot<TAtom>) => T,
+  compare?: (a: T, b: T) => boolean,
+): T
+
+export function useStore<TAtom extends AnyAtom | undefined, T>(
+  atom: TAtom,
+  selector?: (snapshot: AtomSnapshot<TAtom>) => T,
+  compare?: (a: T, b: T) => boolean,
+): T | AtomSnapshot<TAtom> {
+  // When no selector is provided fall back to the identity function so that
+  // callers that were using `useStore(form.store)` without a selector
+  // (as was valid in prior releases) continue to work.
+  return _useStore(
+    atom,
+    (selector ?? ((s: any) => s)) as (snapshot: AtomSnapshot<TAtom>) => T,
+    compare,
+  )
+}