Fix /setup unreachable for unauthenticated users

The proxy treated /setup as a protected route, redirecting unauthenticated
users to /login. This made first-run TMDB onboarding unreachable since
no users exist yet. Add /setup to public auth routes.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

proxy.ts

@@ -1,7 +1,7 @@
 import { getSessionCookie } from "better-auth/cookies";
 import { type NextRequest, NextResponse } from "next/server";
 
-const authRoutes = new Set(["/login", "/register"]);
+const authRoutes = new Set(["/login", "/register", "/setup"]);
 
 export function proxy(request: NextRequest) {
   const sessionCookie = getSessionCookie(request);