Draft Contracts API

Stage contracts for human review instead of creating them directly as active contracts:

• POST /draft-contracts - Create a contract in the "draft" holding state
• GET /draft-contracts/{id}, PUT /draft-contracts/{id}, and DELETE /draft-contracts/{id} - Retrieve, replace, or delete a draft contract
• Compatibility: the existing /pending-contracts endpoints remain available with their current request and response shapes

Draft contracts appear in the Rillet UI under "Draft" for an operator to approve or reject.

Deduplication via external_references: to prevent duplicates on retry, attach at least one external_references entry with a stable (type, id) pair. Re-posting with any matching pair replaces the prior draft record. Draft contracts created without external_references are not deduplicated — every POST creates a new record.

Each reference's type slug must already be defined under Rillet Settings → External References for your organization. References attached at create time are preserved when the draft contract is later promoted to an active contract.

Once a draft contract is approved in the UI it becomes a regular contract.