Update Tenant Integration Tools

Replace the tenant-level deny-list and return the updated tool list.

No validation of names against discovery: a deny-list entry for an unknown tool is a harmless no-op, and validating would couple this write to a live provider API call.

Membership is resolved through next_disabled_tools so a full-state PUT that enables one tool cannot persist a different tool as newly disabled (stale client cache / index mix-up). Last-write-wins otherwise: the writers are the tenant's admins on one settings page, and the response always returns the authoritative post-write state (which the UI renders).