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/allauth/contexts/RouterContext.tsx

@@ -0,0 +1,31 @@
+'use client'
+
+import { createContext, useContext, type ReactNode } from 'react'
+import type { RouterAdapter } from '../adapters/router'
+
+const Context = createContext<RouterAdapter | null>(null)
+
+interface RouterContextProps {
+    children: ReactNode
+    router: RouterAdapter
+}
+
+export function RouterContext({ children, router }: RouterContextProps) {
+    return (
+        <Context value={router}>
+            {children}
+        </Context>
+    )
+}
+
+/**
+ * Hook to access the router adapter.
+ * Must be used within AllauthContext.
+ */
+export function useRouter(): RouterAdapter {
+    const router = useContext(Context)
+    if (!router) {
+        throw new Error('useRouter must be used within AllauthContext')
+    }
+    return router
+}