Use turn environment settings for sandbox execution (#40771)

## Why

Tool execution can use an environment whose sandbox configuration differs from the turn-wide configuration. Sandbox selection and process setup need to follow the environment that owns the tool request.

## What changed

- Source Windows sandbox level, legacy Landlock mode, and Windows private desktop settings from the selected turn environment across tool orchestration, unified exec, patch application, and zsh fork escalation.
- Preserve Windows sandbox level overrides in restorable thread settings and invalidate MCP configuration when that level changes.

## Testing

- Add a resume test that verifies an elevated Windows sandbox override survives thread restoration.

GitOrigin-RevId: 9d8fc46404919f5ae97c9ed712c0932a1f095e36