Add Phase 0: sign-up, login, and profile

- Next.js (App Router) + TypeScript + Tailwind
- Prisma + SQLite for the User model
- Sign-up with 18+ age gate, email/password validation (zod), bcrypt hashing
- Login via NextAuth credentials provider, JWT sessions
- Protected /profile route (view + edit name/bio)

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01VL5YUEf2B9LG4xdVUQwcSg

src/app/api/auth/[...nextauth]/route.ts

@@ -0,0 +1,6 @@
+import NextAuth from "next-auth";
+import { authOptions } from "@/lib/auth";
+
+const handler = NextAuth(authOptions);
+
+export { handler as GET, handler as POST };