Create OrchestratorPingJob for periodic coordination

Create a periodic job that pings the Orchestrator when it has been idle for at least 2 minutes. ## Behavior - Runs every 30 seconds - Checks if Orchestrator agent exists and has status `idle` - Checks if `status_updated_at` is older than 2 minutes - If both conditions true: broadcasts ping to Orchestrator - If not: does nothing (will try again next run) ## Ping Message ```json { "type": "ping", "message": "Check state" } ``` ## Changes Required **New file:** `app/jobs/orchestrator_ping_job.rb` **Schedule:** Add to `config/sidekiq.yml` or `config/schedule.rb` depending on job runner ## Parent Epic #62 - Autonomous Agent Coordination via WebSocket