Move allauth + auth UI to legacy/

allauth/ (44 files) is a django-allauth React UI — a separate concern
from the Mizan protocol. Moved to legacy/ pending extraction into a
standalone mizan-django-allauth package.

Also moved to legacy/:
- client/AuthContext.tsx — generic auth state from /me endpoint
- client/RouterContext.tsx — framework-agnostic router adapter
- client/routing.tsx — UserRoute/StaffRoute/AnonymousRoute guards
- client/nextjs.tsx — Next.js router adapter for auth

These are auth UI infrastructure, not Mizan protocol. The Mizan core
only needs JWT for auth header selection (jwt/ stays — MizanProvider
depends on useJWT() to decide between Bearer and session auth).

Cleaned up re-exports in client/react.ts and vitest aliases.

33 React tests pass.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

legacy/nextjs.tsx

@@ -0,0 +1,72 @@
+'use client'
+
+/**
+ * Next.js adapter for mizan/jwt.
+ *
+ * Usage:
+ * ```tsx
+ * // In layout.tsx
+ * import { NextAuthContext } from 'mizan/jwt/nextjs'
+ *
+ * export default function RootLayout({ children }) {
+ *     return (
+ *         <NextAuthContext user={user}>
+ *             {children}
+ *         </NextAuthContext>
+ *     )
+ * }
+ * ```
+ */
+
+import { type ReactNode } from 'react'
+import { useRouter, usePathname, useSearchParams } from 'next/navigation'
+import type { RouterAdapter } from './RouterContext'
+import { RouterContext } from './RouterContext'
+import { AuthContext, type AuthContextProps } from './AuthContext'
+import type { BaseUser, AuthRoutes } from './types'
+
+/**
+ * Create a RouterAdapter from Next.js App Router hooks.
+ */
+export function useNextRouter(): RouterAdapter {
+    const router = useRouter()
+    const pathname = usePathname()
+    const searchParams = useSearchParams()
+
+    return {
+        push: (path: string) => router.push(path),
+        replace: (path: string) => router.replace(path),
+        pathname,
+        searchParams: new URLSearchParams(searchParams.toString()),
+    }
+}
+
+export interface NextAuthContextProps<TUser extends BaseUser = BaseUser> {
+    children: ReactNode
+    /** Initial user from SSR hydration */
+    user?: TUser | null
+    /** API endpoint to fetch user data (default: '/api/auth/me/') */
+    userEndpoint?: string
+    /** Route configuration for guards */
+    routes?: Partial<AuthRoutes>
+}
+
+/**
+ * Next.js-specific AuthContext that handles the router automatically.
+ */
+export function NextAuthContext<TUser extends BaseUser = BaseUser>({
+    children,
+    user,
+    userEndpoint,
+    routes,
+}: NextAuthContextProps<TUser>) {
+    const router = useNextRouter()
+
+    return (
+        <RouterContext router={router}>
+            <AuthContext user={user} userEndpoint={userEndpoint} routes={routes}>
+                {children}
+            </AuthContext>
+        </RouterContext>
+    )
+}