ci(run): add dedicated run command validation

[GaspardKirira]

Summary

Add focused CI jobs for run planning, script execution, runtime supervision,
watch behavior, and CLI compatibility.

Requirements

• Run on Linux.
• Run on macOS.
• Run on Windows.
• Test direct script compilation.
• Test CMake script fallback.
• Test project execution.
• Test process termination.
• Test runtime arguments and environment.
• Test watch sessions where supported.

Acceptance criteria

• Run tests execute independently from the complete CLI suite.
• Platform-specific failures are visible.
• Direct and fallback paths are validated.
• Runtime lifecycle tests are included.
• Pull requests modifying run code trigger the jobs.