## Why
Background helpers launched from a detached Windows process can allocate console windows. Job Object launches and containment fallbacks need to preserve console suppression as well.
## What changed
- Add `codex_utils_process::background_command` to set `CREATE_NO_WINDOW` on Windows, and use it across background subprocess launches, including Git, plugins, authentication, diagnostics, and sandbox helpers.
- Centralize console suppression in Job Object launches. Keep `CREATE_NO_WINDOW` when retrying without containment, and clear `CREATE_SUSPENDED` so the fallback child can run.
- Preserve console inheritance for interactive shell launches and interactive AWS authentication refreshes.
## Testing
Add Windows regression tests covering console-free launches from detached parents through standard and Tokio commands, stdout/stderr capture, successful containment, Job Object creation and assignment failures, and sandbox setup refresh helpers.
GitOrigin-RevId: b2c238fa7d4f9fbd868e5adf7d4be9958ff01e6c
