feat(canon): add Interface Change Registry concept and workplan
Concept doc captures the design for coordinated API evolution in agent
ecosystems: InterfaceChange entity, draft→published→resolved lifecycle,
TPSC-derived dependency routing, inbox-based notifications, pre-change
coordination via planned_for, and deliberate deferral of webhooks.
CUST-WP-0033 workplan: 6 tasks (model, API, dispatch integration,
MCP tools, dashboard, webhook EP).
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>