#649 Health Check Workflows

Scheduled health monitoring workflows. Workflows on _platform tenant: - _system.health.api - Check API endpoints (every 5 min) - _system.health.workers - Check worker status (every 5 min) - _system.health.db - Check database (every 5 min) - _system.health.report - Daily health report email Uses internal.health.* tools. Registered as scheduled workflows during platform bootstrap. Parent: #639