All 18 integration health endpoints previously proxied to the backend
agent /health with a 3s timeout, causing false reds when agents were
slow but functional. The harness already checks agent reachability
via the agent:<slug> probe. Health endpoints now return a simple 200
confirming the Next.js process is alive.
Delete the pre-generated starters/ directory tree (previously
synced from packages/ by generate-starters.ts). Add
extract-starter.ts which produces a starter tarball on demand
from any integration. Move shared starter template files to
showcase/shared/starter-template/.