🪲 BUG-#246: Run background cleanup regardless of config

[FernandoCelmer]

Description

Modified files:

• dotflow/core/workflow.py — Changed elif self.config: to else: in Manager.__init__. The cleanup thread that joins the background worker and fires on_success/on_failure callbacks is now always started when mode=BACKGROUND, regardless of whether config is provided.
• tests/core/test_workflow.py — Added two new tests covering the fixed scenario: test_background_callback_runs_without_config and test_background_callback_failure_runs_without_config.

Motivation and Context

When running in BACKGROUND mode without a config object (config=None), the original conditional chain fell through both branches — neither _callback_workflow nor the cleanup thread was ever started. This silently swallowed on_success and on_failure callbacks entirely.

Closes #246

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation updated (documentation was updated and published)

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules