feat: remove fluxo de login (NextAuth) e abre direto no dashboard; landing preservada

- pages/_app.jsx: remove SessionProvider/next-auth
- pages/index.jsx: nova rota '/' redireciona para /dashboard (sem auth)
- pages/landing.jsx: index.jsx renomeado e comentado como desativado (preservado)
- pages/dashboard.jsx: remove useSession/signOut, bloco 'Olá/Sair', importa React p/ build
- pages/apps/trendsnews e worldcup2026: remove useSession (não usado no render)
- pages/signin.jsx, signup.jsx, api/auth/[...nextauth].js: preservados com comentário de desativação (sem exclusão)
- next build validado com sucesso

pages/dashboard.jsx

@@ -1,11 +1,10 @@
+import React from "react"
 import { useState } from "react"
 import { useRouter } from "next/router"
-import { useSession, signOut } from "next-auth/react"
 import AvatarSelector from "../components/AvatarSelector"
 import CategoryMenu from "../components/CategoryMenu"
 
 export default function Dashboard() {
-  const { data: session } = useSession()
   const router = useRouter()
   const [selectedAvatar, setSelectedAvatar] = useState("😀")
   const [selectedCategory, setSelectedCategory] = useState("all")
@@ -104,15 +103,6 @@ export default function Dashboard() {
             selectedAvatar={selectedAvatar}
             onSelect={setSelectedAvatar}
           />
-          <span className="text-gray-600">
-            Olá, {session?.user?.name || session?.user?.username || "usuário"}!
-          </span>
-          <button
-            onClick={() => signOut({ callbackUrl: "/" })}
-            className="text-red-600 hover:underline font-medium"
-          >
-            Sair
-          </button>
         </div>
       </nav>