docs: comprehensive README update for open source developers

- Update tech stack versions (Next.js 16, React 19, FastAPI 0.123.7, etc.)
- Fix required vs optional environment variables (Daytona, Tavily, Firecrawl required)
- Clarify optional features (Relace, Vercel deployments, Composio)
- Update Docker ports (frontend 3001, redis 6380)
- Add cloud deployment options (Vercel, Cloud Run, Cloudflare Workers)
- Update architecture diagram with current integrations
- Fix container names (cheatcode-production-*)
- Update clone URL to cheatcode-ai/cheatcode

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: iamjr15