feat(ci): add orchestrator integration tests and plugin interface tests

- Add validate-orchestrator-integration.yml with 3 parallel jobs:
  plugin-interface (unit tests + smoke tests), k8s-integration
  (k3d + localstack), and aws-integration (localstack only)
- Add orchestrator-plugin.test.ts with 15 unit tests covering
  loadOrchestrator() and loadEnterpriseServices() for both
  installed and not-installed states
- Disk space management follows proven patterns from orchestrator
  repo (parallel jobs, aggressive cleanup between tests)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: frostebite