docs(sdk): rewrite integration guide with production examples

Phase 5: Documentation & CDN Setup (1.5h)
- Complete rewrite of docs/integration-guide.md
- GTM-style architecture explanation
- Quick Start (2-minute setup)
- Configuration options and API reference
- Framework integration (React, Vue, Next.js)
- CDN hosting (Cloudflare, S3, self-hosted, GitHub Pages)
- Versioning strategy
- Testing and troubleshooting sections
- Advanced usage examples (e-commerce tracking)
- Privacy & GDPR compliance
- Performance metrics and browser support
- Created sdk/README.md with build/deploy instructions

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: rmarsigli