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

schema/runbook-pack-v0.2.schema.json

@@ -8,7 +8,6 @@
     "id",
     "title",
     "owner",
-    "exercise_status",
     "engine"
   ],
   "additionalProperties": false,
@@ -33,7 +32,8 @@
     },
     "exercise_status": {
       "type": "string",
-      "pattern": "^(unexercised|exercised [0-9]{4}-[0-9]{2}-[0-9]{2} by \\S+)$"
+      "deprecated": true,
+      "description": "Deprecated and ignored. Maturity is derived from run history (docs/maturity-and-projects.md); old packs that still carry this field keep loading."
     },
     "engine": {
       "enum": [