v0.40.0

Session snapshots: a scenario's depends_on chain no longer re-runs the UI login on every cached replay. Windup captures each dependency's exit state (Playwright storageState + final URL) and restores it into a fresh context, skipping the chain (deps≈0). Still verified — a stale snapshot fails verification and falls back to a full-chain replay, never a false pass. Snapshots are gitignored (they hold auth cookies). The big replay-speed win from feedback #4.