Create a playbook definition

Creates a new organization-level playbook definition; it starts in draft status. Authorization: organization administrators only — other callers are rejected with 403. Body: name (required, 1-200 chars); optional description (<=5000 chars); optional spaceTypes (array of space-type slugs the playbook applies to — omit/empty means all space types); optional tasks (<=30 items, each { id (1-64), title (1-200), instructions?, dependsOn? (ids of tasks that must complete first) }); optional actions (<=20 items, each { installedActionId, preApproval?, postApproval?, dependsOn? (task ids only — an action may not depend on another action) } referencing installed actions, with per-action human-approval gates). Response 201: { data: Playbook }.