fix: add React 18-compatible useActionState shim and update imports

[ajphilton]

Summary

This PR adds a small compatibility shim for useActionState so that the
Next.js starter can run correctly on React 18 while the codebase still uses
the React 19-style useActionState API.

React 18 does not yet export useActionState from "react", which causes
build/runtime errors for projects using the current starter.

What this changes

1. New shim utilities

• src/lib/react-compat.ts

  • Adds useActionStateShim, implemented on top of useState +
    useTransition.
  • API shape: [state, dispatch, isPending], matching the React 19
    useActionState tuple.

• src/lib/react-use-action-state-shim.ts

  • Thin wrapper that re-exports the shim as useActionState so components
    can simply do:

    import { useActionState } from "@lib/react-use-action-state-shim"

2. Update imports in components that used useActionState from "react"

Replaced:

import { useActionState } from "react"

with:

import { useActionState } from "@lib/react-use-action-state-shim"

in the following files:
• src/modules/account/components/profile-phone/index.tsx
• src/modules/account/components/profile-billing-address/index.tsx
• src/modules/account/components/profile-name/index.tsx
• src/modules/account/components/profile-password/index.tsx
• src/modules/account/components/address-card/add-address.tsx
• src/modules/account/components/address-card/edit-address-modal.tsx
• src/modules/account/components/profile-email/index.tsx
• src/modules/account/components/login/index.tsx
• src/modules/account/components/register/index.tsx
• src/modules/account/components/transfer-request-form/index.tsx
• src/modules/checkout/components/addresses/index.tsx

No other behaviour changes.

Why this is safe

•	The shim only affects components that were already calling

useActionState, and it matches the expected tuple signature.
• If/when the starter upgrades fully to React 19, this shim can be removed
and the imports swapped back to:

import { useActionState } from "react"

with minimal code churn.

Testing notes

I verified that the project installs and builds with the shim wired in.
I wasn’t able to fully exercise all runtime paths against a real Medusa
backend (publishable key constraints), so CI + your existing test harness
will provide a more robust verification than I can locally.

Happy to adjust naming/locations if you’d prefer these helpers live
somewhere else (e.g. a more general react-compat/hooks module).

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