feat(core)!: introduce runtime extension registry and flat module conventions

BREAKING CHANGE: sup config now derives entries from package.json#exports and a server/client glob instead of manual lists; module structure follows flat + barrel convention with .server.js/.client.js runtime suffixes

src/features/auth/AuthPage.server.js

@@ -1,15 +1,4 @@
-/**
- * Auth Page - Server Component Wrapper for Next.js App Router
- *
- * Default auth UI: login, register, forgot, reset, confirm, logout at /auth/[...auth].
- * Re-export in your app: export { default } from '@zen/core/features/auth/page';
- *
- * For custom auth pages (all flows) that match your site style, use components from
- * '@zen/core/features/auth/components' and actions from '@zen/core/features/auth/actions'.
- * See README-custom-login.md in this package. Basic sites can keep using this default page.
- */
-
-import { AuthPagesClient } from '@zen/core/features/auth/pages';
+import AuthPageClient from './AuthPage.client.js';
 import {
   registerAction,
   loginAction,
@@ -18,16 +7,16 @@ import {
   resetPasswordAction,
   verifyEmailAction,
   setSessionCookie,
-  getSession
-} from '@zen/core/features/auth/actions';
+  getSession,
+} from './actions.js';
 
 export default async function AuthPage({ params, searchParams }) {
   const session = await getSession();
-  
+
   return (
     <div className="min-h-screen flex items-center justify-center p-4 md:p-8">
       <div className="max-w-md w-full">
-        <AuthPagesClient
+        <AuthPageClient
           params={params}
           searchParams={searchParams}
           registerAction={registerAction}