docs: production build optimization

[sarahxsanders]

First guide in the new GraphQL production guide series, focusing specifically on build optimization for production deployments. Content covers:

• Environment variable configuration for GraphQL.js optimization
• Dead code elimination and tree shaking setup
• Browser compatibility handling
• Code splitting strategies
• Build tool configurations for Webpack, Rollup, and esbuild
• Bundle analysis and verification steps

I'd love feedback and a review, but please do not merge until the entire production guide series is ready to ship. The focused guides will replace the production monolith that exists today