fix: use Web Crypto API in middleware (Edge Runtime compat)

app/api/auth/route.ts

@@ -1,5 +1,4 @@
 import { NextResponse } from 'next/server'
-import { cookies } from 'next/headers'
 import * as crypto from 'crypto'
 
 const SECRET = process.env.APP_SECRET || 'smart-home-default-secret-change-me'
@@ -24,7 +23,7 @@ export async function POST(req: Request) {
     secure: true,
     sameSite: 'strict',
     path: '/',
-    maxAge: 60 * 60 * 24 * 365, // 1 year — tablet stays logged in
+    maxAge: 60 * 60 * 24 * 365,
   })
 
   return res