feat: add cache-behavior-playground example (WIP)
Initial scaffold for comprehensive cache behavior demonstration:
- 65 scenarios covering all caching primitives
- Visual components (CacheIndicator, TimestampDisplay, PlatformBadge)
- Platform detection (next start vs Vercel)
- First scenario (A1: use cache basic)
Designed to serve as living documentation comparing:
- next start (self-hosted) vs Vercel behavior
- Automated conformance tests via Vercel Sandbox + Workflows
https://claude.ai/code/session_0134rDLLdGXtt6D41X2yuxbX
