Merge remote-tracking branch 'origin/main' into main

Resolved conflicts:
- .github/workflows/comprehensive-tests.yml: Used their version (new CI workflow)
- cmd/simctl/main.go: Used their version (includes cloud integrations)
- internal/sandbox/command_validator.go: Used their version (whitespace formatting)

Merging:
- Our cleanup: 40+ obsolete files removed, documentation consolidated
- Their work: Cloud integrations (AWS/GCP/Azure), testing infrastructure, PR #39

Both changesets are now integrated.