Retire exercise_status: maturity is the only notion; add CLI tests (RBT-WP-0009-T01)

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

Assistant: claude-code
Assistant-Model: sonnet
Assistant-Process: 295952@bnt-lap001
Assistant-Session: e93f64ad-516c-46eb-9666-aad8d300c477

runbooks/showcase-lighthouse/pack.yaml

@@ -3,7 +3,6 @@ id: rtut.showcase-lighthouse
 title: "Showcase: a night at the lighthouse"
 owner: runbook-tutorials
 outcome: You have played a short interactive story that touches every feature of the runbook engine, using only harmless echo, printf and a scratch file. Nothing outside /tmp/rtut-* is touched.
-exercise_status: unexercised
 engine: native
 parameters:
   - {id: keeper, label: Your keeper's name, type: string, default: Ada, pattern: "[A-Za-z]+", help: One word. Used in the story.}