#643 Platform Bootstrap Workflow

_system.platform.bootstrap workflow for fresh deployment. Workflow runs on _platform tenant, internal queue. Steps: 1. Create platform, demo, test tenants (using internal.platform.create_system_tenant) 2. Init RBAC for all 4 system tenants 3. Create platform owner 4. Register pre-installed apps to marketplace 5. Install apps on all 4 tenants 6. Create default rate limits with schedules and priorities 7. Setup platform secrets 8. Install uptime_app on _platform 9. Mark platform as initialized Triggered automatically on fresh deployment by internal-worker. Parent: #639