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.client.js

@@ -1,12 +1,89 @@
 'use client';
 
-/**
- * Auth Pages Export for Next.js App Router
- * 
- * This exports the auth client components.
- * Users must create their own server component wrapper that imports the actions.
- */
+import { useRouter } from 'next/navigation';
+import { useEffect, useState } from 'react';
+import LoginPage from './pages/LoginPage.client.js';
+import RegisterPage from './pages/RegisterPage.client.js';
+import ForgotPasswordPage from './pages/ForgotPasswordPage.client.js';
+import ResetPasswordPage from './pages/ResetPasswordPage.client.js';
+import ConfirmEmailPage from './pages/ConfirmEmailPage.client.js';
+import LogoutPage from './pages/LogoutPage.client.js';
 
-export { default as AuthPagesClient } from './components/AuthPages.js';
-export { default as AuthPagesLayout } from './components/AuthPagesLayout.js';
+const PAGE_COMPONENTS = {
+  login:    LoginPage,
+  register: RegisterPage,
+  forgot:   ForgotPasswordPage,
+  reset:    ResetPasswordPage,
+  confirm:  ConfirmEmailPage,
+  logout:   LogoutPage,
+};
 
+export default function AuthPage({
+  params,
+  searchParams,
+  registerAction,
+  loginAction,
+  forgotPasswordAction,
+  resetPasswordAction,
+  verifyEmailAction,
+  logoutAction,
+  setSessionCookieAction,
+  redirectAfterLogin = '/',
+  currentUser = null,
+}) {
+  const router = useRouter();
+  const [currentPage, setCurrentPage] = useState(null);
+  const [email, setEmail] = useState('');
+  const [token, setToken] = useState('');
+
+  useEffect(() => {
+    const fromParams = params?.auth?.[0];
+    if (fromParams) { setCurrentPage(fromParams); return; }
+    if (typeof window !== 'undefined') {
+      const match = window.location.pathname.match(/\/auth\/([^\/?]+)/);
+      setCurrentPage(match ? match[1] : 'login');
+    } else {
+      setCurrentPage('login');
+    }
+  }, [params]);
+
+  useEffect(() => {
+    const run = async () => {
+      // searchParams became a Promise in Next.js 15 — resolve both forms.
+      const resolved = searchParams && typeof searchParams.then === 'function'
+        ? await searchParams
+        : searchParams;
+
+      const urlParams = typeof window !== 'undefined'
+        ? new URLSearchParams(window.location.search)
+        : null;
+      setEmail(resolved?.email || urlParams?.get('email') || '');
+      setToken(resolved?.token || urlParams?.get('token') || '');
+    };
+    run();
+  }, [searchParams]);
+
+  const navigate = (page) => router.push(`/auth/${page}`);
+
+  if (!currentPage) return null;
+
+  const Page = PAGE_COMPONENTS[currentPage] || LoginPage;
+  const common = { onNavigate: navigate, currentUser };
+
+  switch (Page) {
+    case LoginPage:
+      return <Page {...common} onSubmit={loginAction} onSetSessionCookie={setSessionCookieAction} redirectAfterLogin={redirectAfterLogin} />;
+    case RegisterPage:
+      return <Page {...common} onSubmit={registerAction} />;
+    case ForgotPasswordPage:
+      return <Page {...common} onSubmit={forgotPasswordAction} />;
+    case ResetPasswordPage:
+      return <Page {...common} onSubmit={resetPasswordAction} email={email} token={token} />;
+    case ConfirmEmailPage:
+      return <Page {...common} onSubmit={verifyEmailAction} email={email} token={token} />;
+    case LogoutPage:
+      return <Page onLogout={logoutAction} onSetSessionCookie={setSessionCookieAction} />;
+    default:
+      return null;
+  }
+}