feat: set up authentication infrastructure with NextAuth.js v5

- Install next-auth@beta, bcryptjs, zod, and @auth/prisma-adapter
- Create auth.ts with credentials provider and JWT session strategy
- Create auth.config.ts for edge-compatible middleware configuration
- Add NextAuth type extensions for session and JWT
- Create API route handler for authentication
- Configure environment variables for NextAuth
- Add AUTH_SETUP.md documentation

Task: 1. Set up authentication infrastructure
Requirements: 1.1, 2.1

.env.example

@@ -0,0 +1,9 @@
+DATABASE_URL="mysql://user:password@host:port/database"
+
+# NextAuth Configuration
+# NEXTAUTH_URL should be your production URL in production
+NEXTAUTH_URL=http://localhost:3000
+
+# Generate a secure secret with: openssl rand -base64 32
+NEXTAUTH_SECRET=your-secret-key-here-please-change-in-production
+AUTH_SECRET=your-secret-key-here-please-change-in-production