chore: retire TODO.md in favour of workplans

Drop the repo-level Todofile; active work lives in workplans/ and State
Hub per ADR-001. Schedule prepare now surfaces workplans/ instead of
TODO.md. Gitignore .kaizen/agents/ and .kaizen/metrics/ runtime state.

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Removed
+- **`TODO.md`** — work tracking uses `workplans/` and State Hub (ADR-001); the
+  `keepaTodofile` agent remains available for other projects
+
 ### Added
 - **`metrics record --emit-event`** — publishes `kaizen.metrics.recorded` NATS
   envelope for activity-core event-driven definitions (optional `nats-py` via