docs(naming): rename middleware.md to proxy.md (next 16)

docs/patterns/middleware.md → docs/patterns/proxy.md following
the Next.js 16 proxy.ts rename. Update link in CLAUDE.md.

docs/patterns/proxy.md

@@ -0,0 +1,35 @@
+# Patroon: Proxy (route protection)
+
+In Next.js 16 hernoemd van `middleware.ts` naar `proxy.ts`, functienaam van `middleware` naar `proxy`.
+
+```ts
+// proxy.ts
+import { NextResponse } from 'next/server'
+import type { NextRequest } from 'next/server'
+import { sessionOptions } from '@/lib/session'
+
+const protectedRoutes = ['/dashboard', '/products', '/todos', '/settings']
+const authRoutes = ['/login', '/register']
+
+export function proxy(request: NextRequest) {
+  const path = request.nextUrl.pathname
+  const isProtected = protectedRoutes.some(r => path.startsWith(r))
+  const isAuthRoute = authRoutes.some(r => path.startsWith(r))
+
+  // Cookie-aanwezigheid controleren — volledige sessievalidatie in layout.tsx
+  const hasSession = !!request.cookies.get(sessionOptions.cookieName)?.value
+
+  if (isProtected && !hasSession) {
+    return NextResponse.redirect(new URL('/login', request.url))
+  }
+  if (isAuthRoute && hasSession) {
+    return NextResponse.redirect(new URL('/dashboard', request.url))
+  }
+
+  return NextResponse.next()
+}
+
+export const config = {
+  matcher: ['/((?!api|_next/static|_next/image|favicon.ico).*)'],
+}
+```