feat(capabilities): add write router factory and MCP composition (HUB-WP-0002)

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.

hub_core/schemas/capability.py

@@ -71,6 +71,13 @@ class CapabilityRequestDispute(BaseModel):
     suggested_domain: str | None = None
 
 
+class CapabilityRequestReroute(BaseModel):
+    note: str
+    rerouted_by: str
+    domain: str | None = None
+    catalog_entry_id: uuid.UUID | None = None
+
+
 class CapabilityRequestRead(BaseModel):
     model_config = ConfigDict(from_attributes=True)