Approve a pending award or incentive approval request. Resolves the
current approval level (or a specific level by position), enforces the
peer-race guard, and runs the same Approval service every other decision
entry point uses. Returns the updated approval request with the full inbox
view (attachment, review log, approvers). On an idempotent same-user re-click
returns success with reason 'already_decided'.

Required OAuth scope: awards:administer