CHW-1409 EnterpriseSalesOnly

Authentication & Authorization Updated

the Enterprise plan is sold by signed agreement; contact sales@chain305.com

Default message: the Enterprise plan is sold by signed agreement; contact sales@chain305.com
HTTP status: 403 (client)
Reason: SALES_AGREEMENT_REQUIRED

Problem. /api/billing/checkout refused a request for the Enterprise plan with 403. Cause. Enterprise includes a contractual 99.9% uptime service level, so it is sold only under a signed order form and never through self-serve checkout. Signup with plan_id=unlimited likewise starts the org on Free, and /api/billing/plans does not expose an Enterprise Paddle price. Fix. Contact sales@chain305.com; once the order form is signed an operator assigns the plan to the org. HTTP 403.