Phase 1 (rename DB) commit 1b: same attribute->physical column shim as
1a, applied to the document_files satellite model. ORM attribute name
unchanged; FK target string left for the searchspaces rename commit.
- Replaced environment variable usage with a centralized configuration system in multiple modules, including `celery_app`, `agent_cache_store`, `sandbox`, `file_storage`, and `connector_service`.
- Enhanced maintainability and readability by sourcing configuration values from the `config` module instead of directly from environment variables.
- Updated relevant settings to ensure consistent access to configuration values across the application.
