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

.env.example

@@ -0,0 +1,3 @@
+DATABASE_URL="file:./dev.db"
+NEXTAUTH_SECRET="replace-this-with-a-long-random-string"
+NEXTAUTH_URL="http://localhost:3000"