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.

docs/integrations/kaizen-schedule-prepared-event.md

@@ -35,7 +35,7 @@ NATS/event-bus subject, sibling to the existing `kaizen.metrics.recorded` and
     "agent_prompt_found": true,
     "has_memory": true,
     "has_metrics": true,
-    "pointers": ["scope", "todo"],
+    "pointers": ["scope", "workplans"],
     "bytes": 8421
   },
   "session_close": [
@@ -60,7 +60,7 @@ NATS/event-bus subject, sibling to the existing `kaizen.metrics.recorded` and
 | `bundle.agent_prompt_found` | bool | Mirrors `schedule prepare --format json` |
 | `bundle.has_memory` | bool | Memory file present |
 | `bundle.has_metrics` | bool | Metrics summary present |
-| `bundle.pointers` | string[] | Repo pointer labels found (`scope`, `todo`) |
+| `bundle.pointers` | string[] | Repo pointer labels found (`scope`, `workplans`) |
 | `bundle.bytes` | int | Rendered bundle size |
 | `session_close` | string[] | Suggested close commands |