- Inline NextAuth v4 handler directly in `[...nextauth]/route.ts`, removing
the `@/lib/auth/nextauth` abstraction layer
- Add Google/Facebook providers with JWT/session callbacks that expose
`idToken` and `accessToken` on the session for backend exchange
- Refactor `AuthPlatform` from constructor-based to static methods
(`googleSignIn()` / `facebookSignIn()`)
- Update `auth-machine.ts` and layout comment reference to match new structure
- Align with original Dart `nextauth-helpers.{googleLogin, facebookLogin}()`
naming and keep persistence concerns (unstorage, backend, custom cookies)
out of scope for this iteration
Wire the Google/Facebook OAuth callback flow end-to-end so the provider's id_token (Google) and access_token (Facebook) captured by NextAuth are forwarded to the backend in exchange for business tokens:
- Extend the NextAuth config with jwt/session callbacks that surface `account.id_token` / `account.access_token` to the client during first sign-in
- Add an `OAuthSessionSync` bridge mounted inside `RootProviders` that listens to `useSession()` and dispatches new `AuthGoogleSyncSubmitted` / `AuthFacebookSyncSubmitted` events
- Add corresponding actors in the auth XState machine that call `authRepository.googleLogin` / `facebookLogin`, persisting the backend's `LoginResponse` through the existing repository path
This keeps all authentication orchestrated by the auth state machine while preserving NextAuth's OAuth redirect UX.
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