Retrofit Redis caching into an existing project scaffolded with nextjs-trpc-prisma-starter. Use this when the user wants to add Redis, add a cache layer, speed up frequent reads, share cache across processes, or any 'add caching to this project' request. Adds ioredis, a docker-compose redis service, a typed cache helper at src/server/lib/cache.ts, REDIS_URL env, and updates CLAUDE.md to reflect the new dependency. Refuses to run on projects that don't have the scaffolded structure.
