Creates a new statement_request row in PENDING state, opens a Jira issue via Nexus, and transitions the row to CREATED (or FAILED on Jira error). The partial unique index statement_request_one_active_per_partner enforces that a partner can only have one open request at a time — concurrent calls return 409 with the existing Jira issue key in details.existingKey.

Access: Auth methods: JWT bearer. Requires any permission: partner:admin, partner:finance. Partner scope: partnerId from query.