Add create_capability_request_write_router with host workflow callbacks,
CapabilityRequestReroute schema, HubCoreMCPServer.attach_to() with CORE_TOOL_NAMES
exclude filtering, tests, and mark HUB-WP-0002 finished.
Extract the first reusable slice (models, schemas, routers, MCP, migrations)
from state-hub with INTENT/SCOPE, agent instructions, workplan, and aligned
inter_hub capability registry index.
