This PR launches the DevFlow marketing site on main

[craigcallen]

Summary

This PR launches the DevFlow marketing site on main, including the public landing page, waitlist flow, SEO groundwork, and deployment pipeline. It also refines the site content and presentation so the product story, MCP positioning, and browser experience feel more polished and tangible.

Changes

• Add the initial Vite + React + TypeScript + Tailwind CSS v4 marketing site with all core landing page sections
• Wire email capture to Resend through an AWS Lambda function URL
• Add S3 + CloudFront deployment via GitHub Actions following the existing craigcallen.com pattern
• Configure intelligent cache headers and CloudFront invalidation on deploy
• Add SEO metadata, structured data, sitemap, and robots.txt
• Rebrand the landing page with updated typography, colors, assets, and Font Awesome icons
• Rewrite the README as a product landing page and point GitHub nav/footer links to the README
• Improve marketing copy and layout to better communicate workflow, skills, pain points, and MCP's zero-context advantage
• Smooth section transitions, reduce visual borders, preserve typed easing values, and fix hero overflow/browser theming issues
• Remove unnecessary CORS handling from the waitlist Lambda

Test Notes

• Verify the marketing site builds successfully in CI and deploys on push to main
• Smoke test responsive layout, hero section behavior, navigation links, and browser light/dark theming
• Confirm waitlist submission works end to end and SEO artifacts (sitemap.xml, robots.txt, meta tags) are present