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/RouterContext.tsx

@@ -0,0 +1,43 @@
+'use client'
+
+import { createContext, useContext, type ReactNode } from 'react'
+
+/**
+ * Framework-agnostic router adapter.
+ * Implement this interface for your framework (Next.js, Remix, etc.)
+ */
+export interface RouterAdapter {
+    /** Navigate to a path (adds to history) */
+    push: (path: string) => void
+    /** Replace current path (no history entry) */
+    replace: (path: string) => void
+    /** Current pathname (e.g., "/account/login") */
+    pathname: string
+    /** Current search params */
+    searchParams: URLSearchParams
+    /** Get a specific route param (e.g., from /auth/[...path]) - optional */
+    getParam?: (name: string) => string | string[] | undefined
+}
+
+const Context = createContext<RouterAdapter | null>(null)
+
+interface RouterContextProps {
+    children: ReactNode
+    router: RouterAdapter
+}
+
+/**
+ * Provides router adapter to route guards.
+ */
+export function RouterContext({ children, router }: RouterContextProps) {
+    return <Context value={router}>{children}</Context>
+}
+
+/**
+ * Hook to access router adapter.
+ */
+export function useRouter(): RouterAdapter {
+    const ctx = useContext(Context)
+    if (!ctx) throw new Error('useRouter must be used within RouterContext')
+    return ctx
+}