Move the NextAuth v4 configuration from the route handler
(src/app/api/auth/[...nextauth]/route.ts) into a dedicated module
(src/lib/auth/auth.ts) to establish a single source of truth. The
route file now simply re-exports the handler from the shared
module, keeping provider setup, JWT/session callbacks, and
environment variable references in one reusable location.
- 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
Migrate from function-based social login helpers (`facebookLogin`, `googleLogin`)
to class-based services (`new FacebookLogin().signIn()`, `new GoogleLogin().signIn()`),
updating call sites in `AuthFacebookPanel` and `SplashButton` with try/catch error
handling. The NextAuth route handler is also refactored to the v4 pattern, importing
pre-built `GET` / `POST` exports from `@/lib/auth/nextauth` instead of constructing
the handler inline with `NextAuth(authOptions)`.
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