Add a trigger to an automation

Provide exactly one schedule: a frequency cron expression for recurring runs, every_seconds for a fixed interval, or a scheduled_at timestamp for a one-time run. More than one returns 400 schedule_conflict. every_seconds must be a positive integer (400 invalid_every_seconds); values from 1 to 59 are raised to the 60-second minimum, returned as every_seconds: 60 with a schedule_interval_raised entry in warnings. Only the automation's creator can change it; workspace owners and admins can pause or delete it. Anyone else receives 403 automation_owner_only. A system automation (include=system) is changed only by workspace owners and admins (403 workspace_agent_admin_only); any member may add a trigger to it, which runs as that member, and remove their own triggers.

_{Scope: automations:write}