Move hashline_edit out of experimental so it is a stable top-level config with default-on runtime behavior and explicit disable support. Add migration and tests to preserve existing experimental.hashline_edit users without breaking configs.
- Added a new configuration option `disable_omo_env` to control the injection of the `<omo-env>` block in agent prompts.
- Updated relevant functions and tests to support this feature, ensuring that the environment context can be toggled on or off as needed.
- Enhanced documentation to reflect the new option and its implications for API cost and cache hit rates.