Chameleon

Added

• One-command setup: scripts/setup.sh. Collapses "install all the
  requirements" into a single step. It verifies every prerequisite (uv,
  Node 20+, npm, optional Ruby + prism, optional timeout) and prints the
  exact per-OS install command for anything missing, then warms the Python and
  Node environments so the first session is instant instead of building
  mid-edit. --check verifies without installing; --dev adds the test extras
  (pytest, ruff) for contributors. It never installs system packages itself, it
  only reports what to run, so it is safe to re-run. Wired into the install
  guide and CONTRIBUTING.

Changed

• CONTRIBUTING first-time setup uses scripts/setup.sh --dev. The previous
  uv sync one-liner installed runtime deps only and pruned the dev extras,
  leaving a fresh clone without pytest and ruff.

Tests

• The production-tip auto-refresh trigger is now covered. Auto-refresh
  re-derives a production-pinned profile in the background when the locked
  branch's tip moves past the recorded derivation SHA (the freshness signal
  after a teammate merges). That gate previously had no unit test; added one
  for the tip-moved (spawn) and tip-unchanged (no spawn) cases, alongside the
  existing drift, age, migration, and cooldown coverage.