fix: enforce macOS security warnings and exit behavior

- Updated setupDarwinIsolation to require ALLOW_NONLINUX_EXECUTION=1 flag
- macOS execution now exits with error unless explicitly allowed
- Enhanced IsInsideLima() to detect Lima via CLOUD_SAFEGUARD_NO_LIMA=1
- macOS warnings properly suppressed inside Lima environment
- Security warnings shown on native macOS without override flag

Behavior:
- Native macOS: Shows warnings and exits (requires ALLOW_NONLINUX_EXECUTION=1)
- Inside Lima: Warnings suppressed, execution continues
- With override: Shows warnings but allows execution

Fixes: macOS security enforcement and Lima detection
Status: Complete ✅