chore: migrate CLAUDE.md to @-import rule structure (custodian integration)

Register with state-hub under custodian domain. Replace monolithic CLAUDE.md
with thin @-import index; distribute content into .claude/rules/ per ops-bridge pattern.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/rules/repo-boundary.md

@@ -0,0 +1,8 @@
+## Repo boundary
+
+This repo owns **kaizen-agentic** only. It does not own:
+
+- State-hub MCP integration code → `the-custodian/state-hub/mcp_server/server.py`
+- Agent discovery tools (`list_kaizen_agents`, `get_kaizen_agent`) → `the-custodian`
+- Custodian coordination and workplan tracking → `the-custodian`
+- Deployment to custodiancore → `ops-bridge`